<PAGE>   1


                                                    Registration No. 333-_______

     As filed with the Securities and Exchange Commission on August 2, 1999
================================================================================

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                               ------------------

                                  PLEXUS CORP.
             (Exact name of registrant as specified in its charter)

               WISCONSIN                                        39-134447
     (State or other jurisdiction of                          (I.R.S. Employer
      incorporation or organization)                        Identification No.)

          55 JEWELERS PARK DRIVE
            NEENAH, WISCONSIN                                      54957
 (Address of Principal Executive Offices)                        (Zip Code)

                               ------------------

                    SEAMED CORPORATION 1988 STOCK OPTION PLAN
                1995 SEAMED CORPORATION EMPLOYEE STOCK OPTION AND
                                 INCENTIVE PLAN
               1997 SEAMED CORPORATION EMPLOYEE NONQUALIFIED STOCK
                                   OPTION PLAN

                            (Full title of the plan)

                               -------------------

               JOSEPH D. KAUFMAN                              Copy to:
 Vice President, Secretary and General Counsel           KENNETH V. HALLETT
                  PLEXUS CORP.                          Quarles & Brady LLP
             55 Jewelers Park Drive                  411 East Wisconsin Avenue
                  P.O. Box 156                       Milwaukee, Wisconsin 53202
          Neenah, Wisconsin 54957-0156


                     (Name and address of agent for service)

                                 (920) 722-3451
          (Telephone number, including area code, of agent for service)

                               -------------------


<PAGE>   2


<TABLE>
<CAPTION>
                                          CALCULATION OF REGISTRATION FEE
================================================================================================================================
                                                               PROPOSED               PROPOSED
                                                               MAXIMUM                 MAXIMUM
  TITLE OF SECURITIES TO BE          AMOUNT TO BE           OFFERING PRICE            AGGREGATE                AMOUNT OF
         REGISTERED                 REGISTERED (1)            PER SHARE           OFFERING PRICE(2)        REGISTRATION FEE
--------------------------------------------------------------------------------------------------------------------------------
<S>                                 <C>                      <C>                  <C>                      <C>
   Common Stock, par value
       $.01 per share               171,804 shares               (2)                $5,543,513.76              $1,541.10
--------------------------------------------------------------------------------------------------------------------------------
  Preferred Stock Purchase
           Rights                         (3)                    (3)                     (3)                      (3)
================================================================================================================================
</TABLE>

(1)           On July 16, 1999, SeaMED Corporation became a wholly owned
              subsidiary of the Registrant through the merger of a wholly owned
              subsidiary of the Registrant, with and into SeaMED pursuant to an
              Agreement and Plan of Merger by and among the Registrant, SeaMED
              and PS Acquisition Corp. dated as of March 16, 1999. Under the
              Merger Agreement, each share of SeaMED common stock outstanding
              immediately prior to the effective time of the merger was
              converted into 0.4 shares of Plexus common stock. Under the Merger
              Agreement, each outstanding option to purchase shares of SeaMED
              common stock under SEAMED's 1995 Employee Stock Option and
              Incentive Plan, SeaMED's 1997 Employee Nonqualified Stock Option
              Plan, and SeaMED's 1988 Stock Option Plan, each as amended was
              assumed by Plexus and converted into an option to purchase shares
              of Plexus' Common Stock on the same terms and conditions as were
              applicable under the SeaMED option, as adjusted to reflect the
              merger. As a result, Plexus assumed SeaMED options granted under
              the 1995 Plan, the 1997 Plan and the 1988 Plexus Plan covering an
              aggregate of 171,804 shares of Plexus common stock, as adjusted.
              No further options are intended to be granted under the Plans. The
              Plans and the SeaMED options provide for possible adjustment of
              the number, price and kind of shares covered by options granted in
              the event of certain capital or other changes affecting the common
              stock. Pursuant to Rule 416(a) under the Securities Act of 1933,
              this Registration Statement covers, in addition to the above
              171,804 shares of Plexus common stock, an indeterminate number of
              shares that may become subject to the assumed options by means of
              any such adjustment.

(2)           The assumed SeaMED options, as adjusted pursuant to the merger
              agreement, have a weighted average exercise price of $32.2665 per
              share of Plexus common stock. Pursuant to Rule 457(h), the
              aggregate offering price and the registration fee have been
              computed upon the basis of the aggregate exercise price of the
              assumed SeaMED options.

(3)           One right is issued in tandem with each share of Plexus common
              stock. The value attributable to the Preferred Stock Purchase
              Rights is reflected in the market price of the Common Stock to
              which the Rights are attached. Includes registration of shares of
              the Registrant's Preferred Stock and Common Stock underlying such
              rights.


<PAGE>   3


                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(A) PROSPECTUS

         Information specified in Part I of Form S-8 (Items 1 and 2) will be
sent or given to plan participants as specified by Rule 428(b)(1) under the
Securities Act of 1933.


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by Plexus Corp. (the "Registrant")
(Commission File No. 000-44824) with the Securities and Exchange Commission
pursuant to Section 13 of the Securities Exchange Act of 1934, as amended are
incorporated herein by reference:

         (a)      The Registrant's Annual Report on Form 10-K for the fiscal
                  year ended September 30, 1998;

         (b)      The Registrant's Quarterly Reports on Form 10-Q for the
                  quarterly periods ended December 31, 1998 and March 31, 1999;

         (c)      The description of the Common Stock in the Registration
                  Statement on Form 8-A dated July 18, 1986, as amended by
                  Amendment No. 1 thereto dated February 24, 1995;

         (d)      The description of the Preferred Stock Purchase Rights in the
                  Registration Statement on Form 8-K, dated August 17, 1998; and

         (e)      The Registrant's Periodic Report on Form 8-K dated July 23,
                  1999 reporting the SeaMED acquisition.

         All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the 1934 Act, prior to the filing of a
post-effective amendment which indicates that all securities offered hereby have
been sold or which deregisters all securities then remaining unsold, shall be
deemed to be incorporated by reference herein and to be a part hereof from the
date of the filing of such documents.

         Any statement contained in a document incorporated or deemed to be
incorporated by reference herein shall be deemed to be modified or superseded
for purposes hereof to the extent that a statement contained herein or in any
other subsequently filed document which also is or is deemed to be incorporated
by reference herein modifies or supersedes such statement. Any statement so


                                        1
<PAGE>   4


modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part hereof.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.  See Item 3(d) above.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         The legality of the shares of Common Stock registered hereunder will be
passed on for the Registrant by Quarles & Brady LLP, the Registrant's legal
counsel.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         The Registrant is incorporated under the Wisconsin Business Corporation
Law ("WBCL"). Under Section 180.0851(1) of the WBCL, the Registrant is required
to indemnify a director or officer, to the extent such person is successful on
the merits or otherwise in the defense of a proceeding, for all reasonable
expenses incurred in the proceeding if such person was a party because he or she
was a director or officer of the Registrant. In all other cases, the Registrant
is required by Section 180.0851(2) of the WBCL to indemnify a director or
officer against liability incurred in a proceeding to which such person was a
party because he or she was an officer or director of the Registrant, unless it
is determined that he or she breached or failed to perform a duty owed to the
Registrant and the breach or failure to perform constitutes: (i) a willful
failure to deal fairly with the Registrant or its shareholders in connection
with a matter in which the director or officer has a material conflict of
interest; (ii) a violation of criminal law, unless the director or officer had
reasonable cause to believe his or her conduct was lawful or no reasonable cause
to believe his or her conduct was unlawful; (iii) a transaction from which the
director or officer derived an improper personal profit; or (iv) willful
misconduct. Section 180.0858(1) of the WBCL provides that, subject to certain
limitations, the mandatory indemnification provisions do not preclude any
additional right to indemnification or allowance of expenses that a director or
officer may have under the Registrant's articles of incorporation, bylaws, a
written agreement or a resolution of the Board of Directors or shareholders.

         Section 180.0859 of the WBCL provides that it is the public policy of
the State of Wisconsin to require or permit indemnification, allowance of
expenses and insurance to the extent required or permitted under Sections
180.0850 to 180.0858 of the WBCL for any liability incurred in connection with a
proceeding involving a federal or state statute, rule or regulation regulating
the offer, sale or purchase of securities.

         Section 180.0828 of the WBCL provides that, with certain exceptions, a
director is not liable to a corporation, its shareholders, or any person
asserting rights on behalf of the corporation or its shareholders, for damages,
settlements, fees, fines, penalties or other monetary liabilities arising from a
breach of, or failure to perform, any duty resulting solely from his or her
status as a director, unless the person asserting liability proves that the
breach or failure to perform constitutes any of the four exceptions to mandatory
indemnification under Section 180.0851(2) referred to above.

                                        2


<PAGE>   5

         Under Section 180.0833 of the WBCL, directors of the Registrant against
whom claims are asserted with respect to the declaration of an improper dividend
or other distribution to shareholders to which they assented are entitled to
contribution from other directors who assented to such distribution and from
shareholders who knowingly accepted the improper distribution, as provided
therein.

         Article VIII of the Registrant's Bylaws contains provisions that
generally parallel the indemnification provisions of the WBCL and cover certain
procedural matters not dealt with in the WBCL. Directors and officers of the
Registrant are also covered by directors' and officers' liability insurance
under which they are insured (subject to certain exceptions and limitations
specified in the policy) against expenses and liabilities arising out of
proceedings to which they are parties by reason of being or having been
directors or officers.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

         See Exhibit Index following the Signatures page in this Registration
Statement, which Exhibit Index is incorporated herein by reference.

ITEM 9.  UNDERTAKINGS.

         (a)      The undersigned Registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
are being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
                                    Section 10(a)(3) of the Securities Act
                                    of 1933;

                           (ii)     To reflect in the prospectus any facts or
                                    events arising after the effective date of
                                    the Registration Statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the
                                    information set forth in the Registration
                                    Statement. Notwithstanding the foregoing,
                                    any increase or decrease in volume of
                                    securities offered (if the total dollar
                                    value of securities offered would not
                                    exceed that which was registered) and any
                                    deviation from the low or high end of the
                                    estimated maximum offering range may be
                                    reflected in the form of prospectus filed
                                    with the Commission pursuant to Rule 424(b)
                                    if, in the aggregate, the changes in volume
                                    and price represent no more than a 20%
                                    change in the maximum aggregate offering
                                    price set forth in the "Calculation of
                                    Registration Fee" table in the effective
                                    Registration Statement;



                                        3

<PAGE>   6


                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the Registration
                                    Statement or any material change to such
                                    information in the Registration Statement;

                  Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) of
this section do not apply if the Registration Statement is on Form S-3 or Form
S-8, and the information required to be included in a post-effective amendment
by those paragraphs is contained in periodic reports filed by the Registrant
with the Commission pursuant to Section 13 or Section 15(d) of the Securities
Exchange Act of 1934 that are incorporated by reference in the Registration
Statement.

                  (2)   That, for the purpose of determining any liability under
the Securities Act of 1933, each such post-effective amendment shall be deemed
to be a new registration statement re-lating to the securities offered therein,
and the offering of such securities at that time shall be deemed to be the
initial bona fide offering thereof.

                  (3)   To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b)  The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 that is incorporated by reference in the
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

         (h)  Reference is made to the indemnification provisions described in
Item 6 of this Registration Statement.

              Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.


                                        4


<PAGE>   7


                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Neenah, State of Wisconsin, on July 30, 1999.

                                     PLEXUS CORP.
                                     (Registrant)


                                     By: /s/ Peter Strandwitz
                                         ---------------------------------------
                                         Peter Strandwitz,
                                         Chairman and Chief Executive Officer

                               ------------------

                                POWER OF ATTORNEY

         KNOW ALL MEN BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Peter Strandwitz, John L. Nussbaum and
Joseph D. Kaufman, and each of them, his true and lawful attorneys-in-fact and
agents, with full power of substitution and resubstitution, for him and in his
name, place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any other regulatory
authority, granting unto said attorneys-in-fact and agents, and each of them,
full power and authority to do and perform each and every act and thing
requisite and necessary to be done in and about the premises, as fully to all
intents and purposes as he might or could do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents or any of them, or their
substitutes, may lawfully do or cause to be done by virtue hereof.

                              --------------------

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.*

/s/ Peter Strandwitz                       /s/ Harold R. Miller
----------------------------------------   -------------------------------------
Peter Strandwitz, Chairman of the Board,   Harold R. Miller, Director
Chief Executive Office and Director
(Principal Executive Officer)

/s/ John L. Nussbaum                       /s/ Gerald A. Pitner
----------------------------------------   -------------------------------------
John L. Nussbaum, President, Chief         Gerald A. Pitner, Director
Operating Officer and Director

/s/ Thomas P. Sabol                        /s/ Thomas J. Prosser
----------------------------------------   -------------------------------------
Thomas P. Sabol, Chief Financial Officer   Thomas J. Prosser, Director
(Principal Financial Officer)

/s/ Lisa M. Kelley                         /s/ Jan K. Ver Hagen
----------------------------------------   -------------------------------------
Lisa M. Kelley, Treasurer and Principal    Jan K. Ver Hagen, Director
Accounting Officer

/s/ David J. Drury
----------------------------------------
David J. Drury, Director


            *Each of these signatures is affixed as of July 30, 1999.

                                       S-1


<PAGE>   8


                                  PLEXUS CORP.
                               (THE "REGISTRANT")
                          (COMMISSION FILE NO. 0-14553)

                                  EXHIBIT INDEX
                                       TO
                         FORM S-8 REGISTRATION STATEMENT
<TABLE>
<CAPTION>
EXHIBIT                    DESCRIPTION                       INCORPORATED HEREIN BY                FILED HEREWITH
NUMBER                                                             REFERENCE TO
<S>             <C>                                   <C>                                    <C>

4.1             Restated Articles of                  Exhibit 3(i) to Plexus' Annual
                Incorporation of Plexus Corp.,        Report on Form 10-K for the
                as amended through August             year ended September 30, 1998.
                13, 1998

4.2             Bylaws of Plexus Corp., as            Exhibit 3(ii) to Plexus' Quarterly
                amended through November              Report on Form 10-Q for the
                14, 1996                              quarter ended September 30,
                                                      1996.

4.3             Shareholder Rights Plan dated         Exhibit 4.1 to the Registrant's
                as of August 13, 1998 between         Current Report on Form 8-K
                the Registrant and Firstar Trust      dated August 13, 1998.
                Co.

5               Opinion of Counsel                                                                        X

23.1            Consent of                                                                                X
                PricewaterhouseCoopers LLP

23.2            Consent of Counsel                                                            Contained in Opinion
                                                                                              filed as Exhibit 5

23.3            Consent of Ernst & Young                                                                 X
                LLP

24              Powers of Attorney                                                            Signature Page to this
                                                                                              Registration
                                                                                              Statement

</TABLE>



                                      EI-1
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1

                                                    Registration No. 333-_______

     As filed with the Securities and Exchange Commission on August 2, 1999
================================================================================

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                               ------------------

                                  PLEXUS CORP.
             (Exact name of registrant as specified in its charter)

               WISCONSIN                                        39-134447
     (State or other jurisdiction of                          (I.R.S. Employer
      incorporation or organization)                        Identification No.)

          55 JEWELERS PARK DRIVE
            NEENAH, WISCONSIN                                      54957
 (Address of Principal Executive Offices)                        (Zip Code)

                               ------------------

                    SEAMED CORPORATION 1988 STOCK OPTION PLAN
                1995 SEAMED CORPORATION EMPLOYEE STOCK OPTION AND
                                 INCENTIVE PLAN
               1997 SEAMED CORPORATION EMPLOYEE NONQUALIFIED STOCK
                                   OPTION PLAN

                            (Full title of the plan)

                               -------------------

               JOSEPH D. KAUFMAN                              Copy to:
 Vice President, Secretary and General Counsel           KENNETH V. HALLETT
                  PLEXUS CORP.                          Quarles & Brady LLP
             55 Jewelers Park Drive                  411 East Wisconsin Avenue
                  P.O. Box 156                       Milwaukee, Wisconsin 53202
          Neenah, Wisconsin 54957-0156

                     (Name and address of agent for service)

                                 (920) 722-3451
          (Telephone number, including area code, of agent for service)

                               -------------------
2
CALCULATION OF REGISTRATION FEE
================================================================================================================================
                                                               PROPOSED               PROPOSED
                                                               MAXIMUM                 MAXIMUM
  TITLE OF SECURITIES TO BE          AMOUNT TO BE           OFFERING PRICE            AGGREGATE                AMOUNT OF
         REGISTERED                 REGISTERED (1)            PER SHARE           OFFERING PRICE(2)        REGISTRATION FEE
--------------------------------------------------------------------------------------------------------------------------------
Common Stock, par value
       $.01 per share               171,804 shares               (2)                $5,543,513.76              $1,541.10
--------------------------------------------------------------------------------------------------------------------------------
  Preferred Stock Purchase
           Rights                         (3)                    (3)                     (3)                      (3)
================================================================================================================================
(1)           On July 16, 1999, SeaMED Corporation became a wholly owned
              subsidiary of the Registrant through the merger of a wholly owned
              subsidiary of the Registrant, with and into SeaMED pursuant to an
              Agreement and Plan of Merger by and among the Registrant, SeaMED
              and PS Acquisition Corp. dated as of March 16, 1999. Under the
              Merger Agreement, each share of SeaMED common stock outstanding
              immediately prior to the effective time of the merger was
              converted into 0.4 shares of Plexus common stock. Under the Merger
              Agreement, each outstanding option to purchase shares of SeaMED
              common stock under SEAMED's 1995 Employee Stock Option and
              Incentive Plan, SeaMED's 1997 Employee Nonqualified Stock Option
              Plan, and SeaMED's 1988 Stock Option Plan, each as amended was
              assumed by Plexus and converted into an option to purchase shares
              of Plexus' Common Stock on the same terms and conditions as were
              applicable under the SeaMED option, as adjusted to reflect the
              merger. As a result, Plexus assumed SeaMED options granted under
              the 1995 Plan, the 1997 Plan and the 1988 Plexus Plan covering an
              aggregate of 171,804 shares of Plexus common stock, as adjusted.
              No further options are intended to be granted under the Plans. The
              Plans and the SeaMED options provide for possible adjustment of
              the number, price and kind of shares covered by options granted in
              the event of certain capital or other changes affecting the common
              stock. Pursuant to Rule 416(a) under the Securities Act of 1933,
              this Registration Statement covers, in addition to the above
              171,804 shares of Plexus common stock, an indeterminate number of
              shares that may become subject to the assumed options by means of
              any such adjustment.

(2)           The assumed SeaMED options, as adjusted pursuant to the merger
              agreement, have a weighted average exercise price of $32.2665 per
              share of Plexus common stock. Pursuant to Rule 457(h), the
              aggregate offering price and the registration fee have been
              computed upon the basis of the aggregate exercise price of the
              assumed SeaMED options.

(3)           One right is issued in tandem with each share of Plexus common
              stock. The value attributable to the Preferred Stock Purchase
              Rights is reflected in the market price of the Common Stock to
              which the Rights are attached. Includes registration of shares of
              the Registrant's Preferred Stock and Common Stock underlying such
              rights.
3

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(A) PROSPECTUS

         Information specified in Part I of Form S-8 (Items 1 and 2) will be
sent or given to plan participants as specified by Rule 428(b)(1) under the
Securities Act of 1933.

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by Plexus Corp. (the "Registrant")
(Commission File No. 000-44824) with the Securities and Exchange Commission
pursuant to Section 13 of the Securities Exchange Act of 1934, as amended are
incorporated herein by reference:

         (a)      The Registrant's Annual Report on Form 10-K for the fiscal
                  year ended September 30, 1998;

         (b)      The Registrant's Quarterly Reports on Form 10-Q for the
                  quarterly periods ended December 31, 1998 and March 31, 1999;

         (c)      The description of the Common Stock in the Registration
                  Statement on Form 8-A dated July 18, 1986, as amended by
                  Amendment No. 1 thereto dated February 24, 1995;

         (d)      The description of the Preferred Stock Purchase Rights in the
                  Registration Statement on Form 8-K, dated August 17, 1998; and

         (e)      The Registrant's Periodic Report on Form 8-K dated July 23,
                  1999 reporting the SeaMED acquisition.

         All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the 1934 Act, prior to the filing of a
post-effective amendment which indicates that all securities offered hereby have
been sold or which deregisters all securities then remaining unsold, shall be
deemed to be incorporated by reference herein and to be a part hereof from the
date of the filing of such documents.

         Any statement contained in a document incorporated or deemed to be
incorporated by reference herein shall be deemed to be modified or superseded
for purposes hereof to the extent that a statement contained herein or in any
other subsequently filed document which also is or is deemed to be incorporated
by reference herein modifies or supersedes such statement. Any statement so

                                        1
4

modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part hereof.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.  See Item 3(d) above.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         The legality of the shares of Common Stock registered hereunder will be
passed on for the Registrant by Quarles & Brady LLP, the Registrant's legal
counsel.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         The Registrant is incorporated under the Wisconsin Business Corporation
Law ("WBCL"). Under Section 180.0851(1) of the WBCL, the Registrant is required
to indemnify a director or officer, to the extent such person is successful on
the merits or otherwise in the defense of a proceeding, for all reasonable
expenses incurred in the proceeding if such person was a party because he or she
was a director or officer of the Registrant. In all other cases, the Registrant
is required by Section 180.0851(2) of the WBCL to indemnify a director or
officer against liability incurred in a proceeding to which such person was a
party because he or she was an officer or director of the Registrant, unless it
is determined that he or she breached or failed to perform a duty owed to the
Registrant and the breach or failure to perform constitutes: (i) a willful
failure to deal fairly with the Registrant or its shareholders in connection
with a matter in which the director or officer has a material conflict of
interest; (ii) a violation of criminal law, unless the director or officer had
reasonable cause to believe his or her conduct was lawful or no reasonable cause
to believe his or her conduct was unlawful; (iii) a transaction from which the
director or officer derived an improper personal profit; or (iv) willful
misconduct. Section 180.0858(1) of the WBCL provides that, subject to certain
limitations, the mandatory indemnification provisions do not preclude any
additional right to indemnification or allowance of expenses that a director or
officer may have under the Registrant's articles of incorporation, bylaws, a
written agreement or a resolution of the Board of Directors or shareholders.

         Section 180.0859 of the WBCL provides that it is the public policy of
the State of Wisconsin to require or permit indemnification, allowance of
expenses and insurance to the extent required or permitted under Sections
180.0850 to 180.0858 of the WBCL for any liability incurred in connection with a
proceeding involving a federal or state statute, rule or regulation regulating
the offer, sale or purchase of securities.

         Section 180.0828 of the WBCL provides that, with certain exceptions, a
director is not liable to a corporation, its shareholders, or any person
asserting rights on behalf of the corporation or its shareholders, for damages,
settlements, fees, fines, penalties or other monetary liabilities arising from a
breach of, or failure to perform, any duty resulting solely from his or her
status as a director, unless the person asserting liability proves that the
breach or failure to perform constitutes any of the four exceptions to mandatory
indemnification under Section 180.0851(2) referred to above.

                                        2
5

         Under Section 180.0833 of the WBCL, directors of the Registrant against
whom claims are asserted with respect to the declaration of an improper dividend
or other distribution to shareholders to which they assented are entitled to
contribution from other directors who assented to such distribution and from
shareholders who knowingly accepted the improper distribution, as provided
therein.

         Article VIII of the Registrant's Bylaws contains provisions that
generally parallel the indemnification provisions of the WBCL and cover certain
procedural matters not dealt with in the WBCL. Directors and officers of the
Registrant are also covered by directors' and officers' liability insurance
under which they are insured (subject to certain exceptions and limitations
specified in the policy) against expenses and liabilities arising out of
proceedings to which they are parties by reason of being or having been
directors or officers.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

         See Exhibit Index following the Signatures page in this Registration
Statement, which Exhibit Index is incorporated herein by reference.

ITEM 9.  UNDERTAKINGS.

         (a)      The undersigned Registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
are being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
                                    Section 10(a)(3) of the Securities Act
                                    of 1933;

                           (ii)     To reflect in the prospectus any facts or
                                    events arising after the effective date of
                                    the Registration Statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the
                                    information set forth in the Registration
                                    Statement. Notwithstanding the foregoing,
                                    any increase or decrease in volume of
                                    securities offered (if the total dollar
                                    value of securities offered would not
                                    exceed that which was registered) and any
                                    deviation from the low or high end of the
                                    estimated maximum offering range may be
                                    reflected in the form of prospectus filed
                                    with the Commission pursuant to Rule 424(b)
                                    if, in the aggregate, the changes in volume
                                    and price represent no more than a 20%
                                    change in the maximum aggregate offering
                                    price set forth in the "Calculation of
                                    Registration Fee" table in the effective
                                    Registration Statement;

                                        3
6

                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the Registration
                                    Statement or any material change to such
                                    information in the Registration Statement;

                  Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) of
this section do not apply if the Registration Statement is on Form S-3 or Form
S-8, and the information required to be included in a post-effective amendment
by those paragraphs is contained in periodic reports filed by the Registrant
with the Commission pursuant to Section 13 or Section 15(d) of the Securities
Exchange Act of 1934 that are incorporated by reference in the Registration
Statement.

                  (2)   That, for the purpose of determining any liability under
the Securities Act of 1933, each such post-effective amendment shall be deemed
to be a new registration statement re-lating to the securities offered therein,
and the offering of such securities at that time shall be deemed to be the
initial bona fide offering thereof.

                  (3)   To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b)  The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 that is incorporated by reference in the
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

         (h)  Reference is made to the indemnification provisions described in
Item 6 of this Registration Statement.

              Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.

                                        4
7

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Neenah, State of Wisconsin, on July 30, 1999.

                                     PLEXUS CORP.
                                     (Registrant)

                                     By: /s/ Peter Strandwitz
                                         ---------------------------------------
                                         Peter Strandwitz,
                                         Chairman and Chief Executive Officer

                               ------------------

                                POWER OF ATTORNEY

         KNOW ALL MEN BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Peter Strandwitz, John L. Nussbaum and
Joseph D. Kaufman, and each of them, his true and lawful attorneys-in-fact and
agents, with full power of substitution and resubstitution, for him and in his
name, place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any other regulatory
authority, granting unto said attorneys-in-fact and agents, and each of them,
full power and authority to do and perform each and every act and thing
requisite and necessary to be done in and about the premises, as fully to all
intents and purposes as he might or could do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents or any of them, or their
substitutes, may lawfully do or cause to be done by virtue hereof.

                              --------------------

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.*

/s/ Peter Strandwitz                       /s/ Harold R. Miller
----------------------------------------   -------------------------------------
Peter Strandwitz, Chairman of the Board,   Harold R. Miller, Director
Chief Executive Office and Director
(Principal Executive Officer)

/s/ John L. Nussbaum                       /s/ Gerald A. Pitner
----------------------------------------   -------------------------------------
John L. Nussbaum, President, Chief         Gerald A. Pitner, Director
Operating Officer and Director

/s/ Thomas P. Sabol                        /s/ Thomas J. Prosser
----------------------------------------   -------------------------------------
Thomas P. Sabol, Chief Financial Officer   Thomas J. Prosser, Director
(Principal Financial Officer)

/s/ Lisa M. Kelley                         /s/ Jan K. Ver Hagen
----------------------------------------   -------------------------------------
Lisa M. Kelley, Treasurer and Principal    Jan K. Ver Hagen, Director
Accounting Officer

/s/ David J. Drury
----------------------------------------
David J. Drury, Director

            *Each of these signatures is affixed as of July 30, 1999.

                                       S-1
8

                                  PLEXUS CORP.
                               (THE "REGISTRANT")
                          (COMMISSION FILE NO. 0-14553)

                                  EXHIBIT INDEX
                                       TO
                         FORM S-8 REGISTRATION STATEMENT
EXHIBIT                    DESCRIPTION                       INCORPORATED HEREIN BY                FILED HEREWITH
NUMBER                                                             REFERENCE TO
4.1             Restated Articles of                  Exhibit 3(i) to Plexus' Annual
                Incorporation of Plexus Corp.,        Report on Form 10-K for the
                as amended through August             year ended September 30, 1998.
                13, 1998

4.2             Bylaws of Plexus Corp., as            Exhibit 3(ii) to Plexus' Quarterly
                amended through November              Report on Form 10-Q for the
                14, 1996                              quarter ended September 30,
                                                      1996.

4.3             Shareholder Rights Plan dated         Exhibit 4.1 to the Registrant's
                as of August 13, 1998 between         Current Report on Form 8-K
                the Registrant and Firstar Trust      dated August 13, 1998.
                Co.

5               Opinion of Counsel                                                                        X

23.1            Consent of                                                                                X
                PricewaterhouseCoopers LLP

23.2            Consent of Counsel                                                            Contained in Opinion
                                                                                              filed as Exhibit 5

23.3            Consent of Ernst & Young                                                                 X
                LLP

24              Powers of Attorney                                                            Signature Page to this
                                                                                              Registration
                                                                                              Statement
EI-1