<PAGE>
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   FORM 10-K/A


                 Annual report pursuant to Section 13 or 15(d)
                     of the Securities Exchange Act of 1934

                      FOR THE YEAR ENDED DECEMBER 31, 2006
                      ------------------------------------

                          Commission file number 1-1396
                          -----------------------------


                                EATON CORPORATION
             ------------------------------------------------------
             (Exact name of registrant as specified in its charter)


<Table>
<S>                                                             <C>
                        Ohio                                                 34-0196300
           -------------------------------                      -----------------------------------
           (State or other jurisdiction of                      (IRS Employer Identification Number)
           incorporation or organization)

                    Eaton Center
                   Cleveland, Ohio                                           44114-2584
      ----------------------------------------                  -----------------------------------
      (Address of principal executive offices)                               (Zip code)

</Table>


                                 (216) 523-5000
              ----------------------------------------------------
              (Registrant's telephone number, including area code)



          Securities registered pursuant to Section 12(b) of the Act:


<Table>
<S>                                                                   <C>
                                                                          Name of each exchange on
                 Title of each class                                          which registered
            -----------------------------                             -------------------------------
            Common Share ($.50 par value)                                 The New York Stock Exchange
                                                                          The Chicago Stock Exchange
</Table>

Indicate by check mark if the registrant is a well-known seasoned issuer, as
defined in Rule 405 of the Securities Act. Yes X


Indicate by check mark if the registrant is not required to file reports
pursuant to Section 13 or Section 15(d) of the Act. No X

Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months and (2) has been subject to such filing requirements for
the past ninety days. Yes  X

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K.

Indicate by check mark whether the registrant is a large accelerated filer, an
accelerated filer, or a non-accelerated filer.  (Check one): Large accelerated
filer X

Indicate by check mark whether the registrant is a shell company (as defined in
Rule 12b-2 of the Act). No X

                                     Page 1

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The aggregate market value of Common Stock held by non-affiliates of the
registrant as of June 30, 2006 was $11.3 billion.

As of January 31, 2007, there were 146.2 million Common Shares outstanding.


                                EXPLANATORY NOTE
                                ----------------

Eaton Corporation is filing this Amendment No. 1 on Form 10-K/A to its Annual
Report on Form 10-K filed with the Securities and Exchange Commission on
February 28, 2007 (the "Original Report"), solely for the purpose of adding the
conformed signatures of its directors to Exhibit 24, the Power of Attorney. Due
to oversight, the signatures of the directors were not transposed from the
originally executed Power of Attorney to the copy actually filed with the EDGAR
version of the Original Report. Accordingly, a corrected Exhibit 24 is filed
herewith. Except as specifically indicated herein, no other information included
in the Annual Report on Form 10-K for the year ended December 31, 2006 is
amended by this Amendment No. 1 on Form 10-K/A.

                                     Page 2

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ITEM 15.  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES
----------------------------------------------------

    (3)  Exhibits

<TABLE>
<S>               <C>
         24       Power of Attorney - Filed in conjunction with this Form 10-K/A

         31.1     Certification of Form 10-K/A (Pursuant to the Sarbanes-Oxley
                  Act of 2002, Section 302) - Filed in conjunction with this
                  Form 10-K/A

         31.2     Certification of Form 10-K/A (Pursuant to the Sarbanes-Oxley
                  Act of 2002, Section 302) - Filed in conjunction with this
                  Form 10-K/A
</TABLE>

                                     Page 3


<PAGE>

                                   SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the registrant has duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized.


                                             Eaton Corporation
                                             ----------------------------------
                                             Registrant



Date:  March 26, 2007                       /s/ Richard H. Fearon
                                            -----------------------------------
                                            Richard H. Fearon
                                            Executive Vice President -
                                            Chief Financial and Planning Officer



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