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                                                                EXHIBIT 4(f)(13)


                               AMENDMENT NO. 4 TO
                               SECURITY AGREEMENT


                  AMENDMENT NO. 4 TO SECURITY AGREEMENT (this "Amendment"),
dated as of March 12, 2001, among KITTY HAWK FUNDING CORPORATION, a Delaware
corporation, as a secured party (together with its successors and assigns, the
"Company"), CAC FUNDING CORP., a Nevada corporation, as debtor (together with
its successors and assigns, the "Debtor"), CREDIT ACCEPTANCE CORPORATION, a
Michigan corporation, individually and as servicer (together with its successors
and assigns, the "Servicer"), and BANK OF AMERICA, N.A., a national banking
association ("Bank of America"), individually and as collateral agent (together
with its successors and assigns in such capacity, the "Collateral Agent"),
amending that certain Security Agreement (as amended to the date hereof, the
"Security Agreement"), dated as of July 7, 1998, between the Company, the
Debtor, the Servicer and Bank of America (known under the Security Agreement as
"NationsBank, N.A."), individually and as Collateral Agent.

                  WHEREAS, on the terms and conditions set forth herein, the
parties to the Security Agreement wish to amend the Security Agreement as
provided herein.

                  NOW, THEREFORE, the parties hEREBY AGREE AS FOLLOWS:

                  SECTION 1.  DEFINED TERMS.  AS USED IN THIS AMENDMENT
CAPITALIZED TERMS HAVE THE SAME MEANINGS ASSIGNED THERETO IN THE SECURITY
AGREEMENT.

                  SECTION 2.  AMENDMENTS.

         (1)      SECTION 1.1 OF THE SECURITY AGREEMENT IS HEREBY AMENDED BY
DELETING THE DEFINITION OF "INSURANCE POLICY".

         (2)      SECTION 3.4 OF THE SECURITY AGREEMENT IS HEREBY AMENDED BY
DELETING ALL OF THE LANGUAGE IN SUCH SECTION AND REPLACING IT WITH "RESERVED".

         (3)      SECTION 3.5 OF THE SECURITY AGREEMENT IS HEREBY AMENDED BY
DELETING ALL OF THE LANGUAGE IN SUCH SECTION AND REPLACING IT WITH "RESERVED".


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                  SECTION 3.  REPRESENTATIONS AND WARRANTIES.

         (a)      THE DEBTOR HEREBY MAKES TO THE COLLATERAL AGENT, THE COMPANY
AND THE BANK INVESTORS, ON AND AS OF THE DATE HEREOF, ALL OF THE REPRESENTATIONS
AND WARRANTIES SET FORTH IN SECTIONS 3.1 AND 3.2 OF THE SECURITY AGREEMENT,
EXCEPT THAT TO THE EXTENT THAT ANY OF SUCH REPRESENTATIONS AND WARRANTIES
EXPRESSLY RELATE TO AN EARLIER DATE, SUCH REPRESENTATIONS AND WARRANTIES SHALL
BE TRUE AND CORRECT AS OF SUCH EARLIER DATE.

                  SECTION 4. EFFECTIVENESS. THIS AMENDMENT SHALL BECOME
EFFECTIVE ON THE DATE HEREOF.

                  SECTION 5. COSTS AND EXPENSES. THE DEBTOR SHALL PAY ALL OF THE
COMPANY'S, THE BANK INVESTORS' AND THE COLLATERAL AGENT'S COST AND EXPENSES
(INCLUDING OUT OF POCKET EXPENSES AND REASONABLE ATTORNEYS FEES AND
DISBURSEMENTS) INCURRED BY THEM IN CONNECTION WITH THE PREPARATION, EXECUTION
AND DELIVERY OF THIS AMENDMENT.

                  SECTION 6. GOVERNING LAW. THIS AMENDMENT SHALL BE GOVERNED BY
AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

                  SECTION 7. SEVERABILITY; COUNTERPARTS. THIS AMENDMENT MAY BE
EXECUTED IN ANY NUMBER OF COUNTERPARTS AND BY DIFFERENT PARTIES HERETO IN
SEPARATE COUNTERPARTS, EACH OF WHICH WHEN SO EXECUTED SHALL BE DEEMED TO BE AN
ORIGINAL AND ALL OF WHICH WHEN TAKEN TOGETHER SHALL CONSTITUTE ONE AND THE SAME
INSTRUMENT. ANY PROVISIONS OF THIS AMENDMENT WHICH ARE PROHIBITED OR
UNENFORCEABLE IN ANY JURISDICTION SHALL, AS TO SUCH JURISDICTION, BE INEFFECTIVE
TO THE EXTENT OF SUCH PROHIBITION OR UNENFORCEABILITY WITHOUT INVALIDATING THE
REMAINING PROVISIONS HEREOF, AND ANY SUCH PROHIBITION OR UNENFORCEABILITY IN ANY
JURISDICTION SHALL NOT INVALIDATE OR RENDER UNENFORCEABLE SUCH PROVISION IN ANY
OTHER JURISDICTION.

                  SECTION 8. CAPTIONS. THE CAPTIONS IN THIS AMENDMENT ARE FOR
CONVENIENCE OF REFERENCE ONLY AND SHALL NOT DEFINE OR LIMIT ANY OF THE TERMS OR
PROVISIONS HEREOF.

                  SECTION 9. RATIFICATION. EXCEPT AS EXPRESSLY AFFECTED BY THE



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PROVISIONS HEREOF, THE SECURITY AGREEMENT AS AMENDED SHALL REMAIN IN FULL FORCE
AND EFFECT IN ACCORDANCE WITH ITS TERMS AND RATIFIED AND CONFIRMED BY THE
PARTIES HERETO. ON AND AFTER THE DATE HEREOF, EACH REFERENCE IN THE SECURITY
AGREEMENT TO "THIS AGREEMENT", "HEREUNDER", "HEREIN" OR WORDS OF LIKE IMPORT
SHALL MEAN AND BE A REFERENCE TO THE SECURITY AGREEMENT AS AMENDED BY THIS
AMENDMENT.



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                  IN WITNESS WHEREOF, THE PARTIES HERETO HAVE EXECUTED AND
DELIVERED THIS AMENDMENT NO. 4 TO THE SECURITY AGREEMENT AS OF THE DATE FIRST
WRITTEN ABOVE.


                            CAC FUNDING CORP., AS DEBTOR


                            BY: /S/ DOUGLAS W. BUSK
                                NAME: DOUGLAS W. BUSK
                                TITLE: CHIEF FINANCIAL OFFICER


                            CREDIT ACCEPTANCE CORPORATION,
                            INDIVIDUALLY AND AS SERVICER


                            BY: /S/ DOUGLAS W. BUSK
                                -------------------------------------------
                                NAME: DOUGLAS W. BUSK
                                TITLE: CHIEF FINANCIAL OFFICER


                            KITTY HAWK FUNDING CORPORATION,
                             AS COMPANY


                            BY: /S/ ANDY YAN
                                -------------------------------------------
                                NAME:
                                TITLE:


                            BANK OF AMERICA, N.A., INDIVIDUALLY
                            AND AS COLLATERAL AGENT


                            BY: /S/ MICHELLE M. HEATH
                                ------------------------------------------
                                NAME: MICHELLE HEATH
                                TITLE: MANAGING DIRECTOR