Document:

<PAGE>

                                 Exhibit 10.3
                                 ------------

                    PATENT AND TRADEMARK SECURITY AGREEMENT

          THIS PATENT AND TRADEMARK SECURITY AGREEMENT (this "Agreement"), dated
as of September 20, 2001, is made between Amerigon Incorporated, a California
corporation ("Borrower"), and Big Beaver Investments LLC, a Delaware limited
liability company ("Lender").

          Borrower and Lender are parties to that certain Security Agreement
dated as of September 20, 2001 (as amended, modified, renewed or extended from
time to time, the "Security Agreement"), which Security Agreement provides,
among other things, for the grant by Borrower to Lender of a security interest
in all of Borrower's property and assets, including, without limitation, its
patents and patent applications, its trademarks, service marks and trade names,
and its applications for registration of such trademarks, service marks and
trade names. Pursuant to the Security Agreement, Borrower has agreed to execute
and deliver this Agreement to Lender for filing with the United States Patent
and Trademark Office (the "PTO") (and any other relevant recording systems in
any domestic or foreign jurisdiction), and as further evidence of and to
effectuate such assignment of and grant of a security interest in such patents
and patent applications, trademarks, service marks and trade names, and
applications for registration of such trademarks, service marks and trade names,
and the other general intangibles described herein. Accordingly, Borrower and
Lender hereby agree as follows:

          SECTION 1.  DEFINITIONS; INTERPRETATION.

               (a)    All capitalized terms used in this Agreement and not
otherwise defined herein shall have the meanings assigned to them in the
Security Agreement.

               (b)    In this Agreement, (i) the meaning of defined terms shall
be equally applicable to both the singular and plural forms of the terms
defined, and (ii) the captions and headings are for convenience of reference
only and shall not affect the construction of this Agreement.

          SECTION 2.  ASSIGNMENT AND GRANT OF SECURITY INTEREST.

               (a)    As security for the payment and performance of the Secured
Obligations, Borrower hereby assigns, transfers and conveys and grants a
security interest in and mortgage to Lender, for security purposes, all of
Borrower's right, title and interest in, to and under the following property,
whether now existing or owned or hereafter acquired, developed or arising
(collectively, the "Intellectual Property Collateral"):

                      (i)  all foreign and domestic patents and patent
applications, all licenses relating to any of the foregoing and all income and
royalties with respect to any licenses, including, without limitation, such
patents, patent applications and patent licenses as described in
<PAGE>

Schedule A hereto, all rights to sue for past, present and future infringement
----------
thereof, all rights arising therefrom and pertaining thereto, and all reissues,
divisions, continuations, renewals, extensions and continuations-in-part
thereof;

                      (ii)    all state (including common law), federal and
foreign trademarks, service marks and trade names, and applications for
registration of such trademarks, service marks and trade names, all licenses
relating to any of the foregoing and all income and royalties with respect to
any licenses, including, without limitation, such marks, names, applications and
licenses as described in Schedule B hereto, whether registered or unregistered
                         ----------
and wherever registered, whether rights to such marks arise under statutory or
common law, all rights to sue for past, present and future infringement, all
rights arising therefrom and pertaining thereto and all reissues, extensions and
renewals thereof;

                      (iii)   the entire goodwill of or associated with the
businesses now or hereafter conducted by Borrower connected with or symbolized
by any of the aforementioned properties and assets;

                      (iv)    all general intangibles (as defined in the UCC)
and all intangible intellectual or other similar property of Borrower of any
kind or nature, associated with or arising out of any of the aforementioned
properties and assets and not otherwise described above; and

                      (v)     all products and proceeds of any and all of the
foregoing.

               (b)    This Agreement shall create a continuing security interest
in the Intellectual Property Collateral which shall remain in effect until
terminated in accordance with Section 17 hereof.

          SECTION 3.  FURTHER ASSURANCES; APPOINTMENT OF LENDER AS ATTORNEY-IN-
FACT. Borrower at its expense shall execute and deliver, or cause to be executed
and delivered, to Lender any and all documents and instruments, in form and
substance satisfactory to Lender, and take any and all action, which Lender may
reasonably request from time to time, to perfect and continue perfected,
maintain the priority of or provide notice of Lender's security interest in the
Intellectual Property Collateral and to accomplish the purposes of this
Agreement. Lender shall have the right to, in the name of Borrower, or in the
name of Lender or otherwise, without notice to or assent by Borrower, and
Borrower hereby irrevocably constitutes and appoints Lender (and any of Lender's
officers or employees or agents designated by Lender) as Borrower's true and
lawful attorney-in-fact with full power and authority, (i) to sign the name of
Borrower on all or any of such documents or instruments and perform all other
acts that Lender deems necessary or advisable in order to perfect or continue
perfected, maintain the priority or enforceability of or provide notice of
Lender's security interest in, the Intellectual Property Collateral, and (ii) to
execute any and all other documents and instruments, and to perform any and all
acts and things for and on behalf of Borrower, which Lender may deem necessary
or advisable to maintain, preserve and protect the Intellectual Property
Collateral and to accomplish the purposes of this Agreement, including, without
limitation, (A) to defend, settle, adjust or (after the occurrence and during
the continuance of any Event of Default) institute any action, suit or
proceeding with respect to the Intellectual Property Collateral, and, after the
occurrence and during the continuance of any Event of Default, (B) to assert or
retain

                                       2
<PAGE>

any rights under any license agreement for any of the Intellectual Property
Collateral, including, without limitation, any rights of Borrower arising under
Section 365(n) of the Bankruptcy Code, and (C) after the occurrence and during
the continuance of any Event of Default, to execute any and all applications,
documents, papers and instruments for Lender to use the Intellectual Property
Collateral, to grant or issue any exclusive or non-exclusive license or sub-
license with respect to any Intellectual Property Collateral, and to assign,
convey or otherwise transfer title in or dispose of the Intellectual Property
Collateral; provided, however, that in no event shall Lender have the unilateral
power, prior to the occurrence and continuation of an Event of Default, to
assign any of the Intellectual Property Collateral to any Person, including
itself, without Borrower's written consent. The foregoing shall in no way limit
Lender's rights and remedies upon or after the occurrence and during the
continuance of an Event of Default. The power of attorney set forth in this
Section 3, being coupled with an interest, is irrevocable, so long as this
Agreement shall not have terminated in accordance with Section 17.

          SECTION 4.  FUTURE RIGHTS. Except as otherwise expressly agreed to in
writing by Lender, if and when Borrower shall obtain rights to any new
patentable inventions or any new trademarks, or become entitled to the benefit
of any of the foregoing, or obtain rights or benefits with respect to any
reissue, division, continuation, renewal, extension or continuation-in-part of
any patents or trademarks or, or any improvement of any patent, the provisions
of Section 2 shall automatically apply thereto and Borrower shall give to Lender
prompt notice thereof. Borrower shall do all things deemed necessary or
advisable by Lender to ensure the validity, perfection, priority and
enforceability of the security interests of Lender in such future acquired
Intellectual Property Collateral. Borrower hereby authorizes Lender to modify,
amend, or supplement the Schedules hereto and to reexecute this Agreement from
time to time on Borrower's behalf and as its attorney-in-fact to include any
such future Intellectual Property Collateral and to cause such reexecuted
Agreement or such modified, amended or supplemented Schedules to be filed with
PTO.

          SECTION 5.  LENDER'S DUTIES. Notwithstanding any provision contained
in this Agreement, Lender shall have no duty to exercise any of the rights,
privileges or powers afforded to it and shall not be responsible to Borrower or
any other Person for any failure to do so or delay in doing so. Except for the
accounting for moneys actually received by Lender hereunder or in connection
herewith, Lender shall have no duty or liability to exercise or preserve any
rights, privileges or powers pertaining to the Intellectual Property Collateral.

          SECTION 6.  REPRESENTATIONS AND WARRANTIES.  Borrower represents and
warrants to Lender that:

               (a)    A true and correct list of all of the existing
Intellectual Property Collateral consisting of United States patents and patent
applications and/or registrations owned by Borrower, in whole or in part, and
all licenses relating to any of the foregoing, is set forth in Schedule A
                                                               ----------
hereto.

               (b)    A true and correct list of all of the existing
Intellectual Property Collateral consisting of United States trademarks,
trademark registrations and/or applications owned or used by Borrower, in whole
or in part, and all licenses relating to any of the foregoing, is set forth in
Schedule B hereto.
----------

                                       3
<PAGE>

               (c)    All material patents, trademarks, service marks and trade
names of Borrower are subsisting and have not been adjudged invalid or
unenforceable in whole or in part.

               (d)    All maintenance fees at the large entity rate required to
be paid on account of any patents or trademarks of Borrower have been timely
paid for maintaining such patents and trademarks in force, and, to the best of
Borrower's knowledge, each of the patents and trademarks constituting part of
the Intellectual Property Collateral is valid and enforceable in all material
respects.

               (e)    To the best of Borrower's knowledge after due inquiry, no
material infringement or unauthorized use presently is being made of any
Intellectual Property Collateral by any Person.

               (f)    Borrower is the sole and exclusive owner of the
Intellectual Property Collateral and the past, present and contemplated future
use of such Intellectual Property Collateral by Borrower has not, does not and
will not infringe or violate any right, privilege or license agreement of or
with any other Person, in any material respect.

          SECTION 7.  COVENANTS.

               (a)    Borrower will appear in and defend any action, suit or
proceeding which may affect to a material extent its title to, or Lender's
rights or interest in, the Intellectual Property Collateral.

               (b)    Borrower will not allow or suffer any material
Intellectual Property Collateral to become abandoned, nor any registration
thereof to be terminated, forfeited, expired or dedicated to the public.

               (c)    Borrower will diligently prosecute all applications for
patents and trademarks, and file and prosecute any and all continuations,
continuations-in-part, applications for reissue, applications for certificate of
correction and like matters as shall be reasonable and appropriate in accordance
with prudent business practice, and promptly pay any and all maintenance,
license, registration and other fees, taxes and expenses incurred in connection
with any Intellectual Property Collateral.

          SECTION 8.  LENDER'S RIGHTS AND REMEDIES.

               (a)    Lender shall have all rights and remedies available to it
under the Security Agreement, the other Loan Documents and applicable law with
respect to the security interests in any of the Intellectual Property Collateral
or any other collateral. Borrower agrees that such rights and remedies include,
but are not limited to, the right of Lender as a secured party to sell or
otherwise dispose of its collateral after default pursuant to the UCC. Borrower
agrees that Lender shall at all times have such royalty free licenses, to the
extent permitted by law and Borrower's existing contracts, for any Intellectual
Property Collateral that shall be reasonably necessary to permit the exercise of
any of Lender's rights or remedies upon or after the occurrence and during the
continuance of an Event of Default and shall additionally, effective upon or
after the occurrence and during the continuance of an Event of Default, have the
right to license and/or sublicense any Intellectual Property Collateral, whether
general, special or

                                       4
<PAGE>

otherwise, and whether on an exclusive or a nonexclusive basis, any of the
Intellectual Property Collateral, throughout the world for such term or terms,
on such conditions, and in such manner, as Lender in its discretion shall
determine. In addition to and without limiting any of the foregoing, upon the
occurrence and during the continuance of an Event of Default, Lender shall have
the right but shall in no way be obligated to bring suit, or to take such other
action as Lender deems necessary or advisable, in the name of Borrower or
Lender, to enforce or protect any of the Intellectual Property Collateral, in
which event Borrower shall, at the request of Lender, do any and all lawful acts
and execute any and all documents required by Lender in aid of such enforcement.
To the extent that Lender shall elect not to bring suit to enforce such
Intellectual Property Collateral, Borrower agrees to use all reasonable measures
and its diligent efforts, whether by action, suit, proceeding or otherwise, to
prevent the infringement, misappropriation or violations thereof in any material
respect by others and for that purpose agrees diligently to maintain any action,
suit or proceeding against any Person necessary to prevent such infringement,
misappropriation or violation.

               (b)    The cash proceeds actually received from the sale or other
disposition or collection of Intellectual Property Collateral, and any other
amounts received in respect of the Intellectual Property Collateral the
application of which is not otherwise provided for herein, shall be applied as
provided in the Security Agreement.

          SECTION 9.  NOTICES.  All notices or other communications hereunder
shall be in writing (including by facsimile transmission) shall be mailed, sent
or delivered in accordance with the Security Agreement at or to their respective
addresses or facsimile numbers set forth below their names on the signature
pages hereof, or at or to such other address or facsimile number as shall be
designated by any party in a written notice to the other parties hereto.  All
such notices and other communications shall be effective as provided in the
Security Agreement.

          SECTION 10. NO WAIVER; CUMULATIVE REMEDIES. No failure on the part of
Lender to exercise, and no delay in exercising, any right, remedy, power or
privilege hereunder shall operate as a waiver thereof, nor shall any single or
partial exercise of any such right, remedy, power or privilege preclude any
other or further exercise thereof or the exercise of any other right, remedy,
power or privilege. The rights and remedies under this Agreement are cumulative
and not exclusive of any rights, remedies, powers and privileges that may
otherwise be available to Lender.

          SECTION 11. COSTS AND EXPENSES; INDEMNITY.

               (a)    Borrower agrees to pay on demand all costs and expenses of
Lender, including without limitation all reasonable attorneys' fees, in
connection with the enforcement or attempted enforcement of, and preservation of
any rights or interests under, this Agreement, and the assignment, sale or other
disposal of any of the Intellectual Property Collateral.

               (b)    Borrower hereby agrees to indemnify Lender and any of its
affiliates, and their respective directors, officers, employees, agents, counsel
and other advisors (each an "Indemnified Person") against, and hold each of them
harmless from, any and all liabilities, obligations, losses, claims, damages,
demands, penalties, actions, judgments, suits, costs, expenses or disbursements
of any kind or nature whatsoever, including, without limitation,

                                       5
<PAGE>

reasonable attorneys' fees and attorneys' fees incurred pursuant to Chapter 11
United States Code, which may be imposed on, incurred by, or asserted against
any Indemnified Person, in any way relating to or arising out of this Agreement,
including in connection with any infringement or alleged infringement with
respect to any Intellectual Property Collateral, or any action taken or omitted
to be taken by it hereunder (the "Indemnified Liabilities"); provided that
Borrower shall not be liable to any Indemnified Person for any portion of such
Indemnified Liabilities to the extent they are found by a final decision of a
court of competent jurisdiction to have resulted from such Indemnified Person's
gross negligence or willful misconduct. If and to the extent that the foregoing
indemnification is for any reason held unenforceable, Borrower agrees to make
the maximum contribution to the payment and satisfaction of each of the
Indemnified Liabilities which is permissible under applicable law.

               (c)    Any amounts payable to Lender under this Section 11 or
otherwise under this Agreement if not paid upon demand shall bear interest from
the date of such demand until paid in full, at the rate of interest set forth in
the Note.

          SECTION 12. BINDING EFFECT; ASSIGNMENT. This Agreement shall be
binding upon, inure to the benefit of and be enforceable by Borrower, Lender and
their respective permitted successors and permitted assigns. Borrower shall not
have the right to assign its rights or obligations or any interest herein
without the prior written consent of Lender. Lender reserves the right freely to
sell, assign, transfer or grant participations in all or any portion of Lender's
rights and obligations hereunder (i) to one or more Affiliates of Lender and/or
(ii) with the prior consent of Borrower (which consent shall not be unreasonably
withheld) to any other Person.

          SECTION 13. GOVERNING LAW. This Agreement shall be governed by, and
construed in accordance with, the law of the State of California, except to the
extent that the validity or perfection of the assignment and security interests
hereunder in respect of any Intellectual Property Collateral are governed by
federal law and except to the extent that Lender shall have greater rights or
remedies under federal law, in which case such choice of California law shall
not be deemed to deprive Lender of such rights and remedies as may be available
under federal law.

          SECTION 14. ENTIRE AGREEMENT; AMENDMENT. This Agreement and the other
Loan Documents contain the entire agreement of the parties with respect to the
subject matter hereof and shall not be amended except by the written agreement
of the parties as provided in the Security Agreement.

          SECTION 15. SEVERABILITY. Whenever possible, each provision of this
Agreement shall be interpreted in such manner as to be effective and valid under
all applicable laws and regulations. If, however, any provision of this
Agreement shall be prohibited by or invalid under any such law or regulation in
any jurisdiction, it shall, as to such jurisdiction, be deemed modified to
conform to the minimum requirements of such law or regulation, or, if for any
reason it is not deemed so modified, it shall be ineffective and invalid only to
the extent of such prohibition or invalidity without affecting the remaining
provisions of this Agreement, or the validity or effectiveness of such provision
in any other jurisdiction.

                                       6
<PAGE>

          SECTION 16. COUNTERPARTS. This Agreement 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
taken together shall constitute one and the same agreement.

          SECTION 17. TERMINATION. Upon payment and performance in full of all
Secured Obligations, this Agreement shall terminate and Lender shall promptly
execute and deliver to Borrower such documents and instruments reasonably
requested by Borrower as shall be necessary to evidence termination of all
security interests given by Borrower to Lender hereunder, including cancellation
of this Agreement by written notice from Lender to the PTO; provided, however,
that (i)the obligations of Borrower under Section 11 hereof shall survive such
termination and (ii) in the event a voluntary proceeding in bankruptcy is filed
by Borrower or an involuntary proceeding in bankruptcy is filed against
Borrower, this Agreement and Lender's interest in the Intellectual Property
Collateral created hereby shall survive such proceeding.

          SECTION 18. SECURITY AGREEMENT. Borrower acknowledges that the rights
and remedies of Lender with respect to the security interests in the
Intellectual Property Collateral granted hereby are more fully set forth in the
Security Agreement and the other Loan Documents and all such rights and remedies
are cumulative.

          SECTION 19. NO INCONSISTENT REQUIREMENTS. Borrower acknowledges that
this Agreement and the Security Agreement may contain covenants and other terms
and provisions variously stated regarding the same or similar matters, and
Borrower agrees that all such covenants, terms and provisions are cumulative and
all shall be performed and satisfied in accordance with their respective terms.

        [Remainder of page left intentionally blank; signatures follow]

                                       7
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have duly executed this Patent
and Trademark Security Agreement, as of the date first above written.

                                                BORROWER:

                                                AMERIGON INCORPORATED, a
                                                California corporation

                                                By: /s/ Richard A. Weisbart
                                                   -----------------------------
                                                   Richard A. Weisbart,
                                                   President and CEO

                                                Address:
                                                5462 Irwindale Avenue
                                                Irwindale, California  91706
                                                Attn:  Richard A. Weisbart
                                                     ---------------------------
                                                Fax:  (626) 815-7441
                                                     ---------------------------

                                                LENDER:

                                                BIG BEAVER INVESTMENTS LLC, a
                                                Delaware limited liability
                                                company

                                                By:  /s/ O. B. Marx, III
                                                   -----------------------------
                                                   Name:  Oscar B. Marx, III
                                                         -----------------------
                                                   Title: President
                                                         -----------------------

                                                Address:
                                                801 W. Big Beaver Road, Suite
                                                201
                                                Troy, Michigan 48084
                                                Attn: President
                                                     ---------------------------
                                                Fax: (248) 362-3033
                                                    ----------------------------

                                       8<PAGE>

                                 Exhibit 10.4
                                 ------------

                          CONVERTIBLE PROMISSORY NOTE

$1,500,000                                                    September 20, 2001
                                                           Irwindale, California

          FOR VALUE RECEIVED, Amerigon Incorporated, a California corporation
(the "Borrower"), promises to pay to the order of Big Beaver Investments LLC, a
      --------
Delaware limited liability company (the "Lender"), the principal amount of One
                                         ------
Million Five Hundred Thousand Dollars ($1,500,000), or, if less, the aggregate
principal amount of the Loan Advances (as defined in the Credit Agreement
referred to below) made by the Lender to the Borrower pursuant to the Credit
Agreement.

          The Borrower also promises to pay interest on the unpaid principal
amount hereof from the date hereof until paid at the rates and at the times
which shall be determined in accordance with the provisions of the Credit
Agreement. Any interest not paid when due shall be compounded and shall
thereafter accrue interest at the rates and at the times which shall be
determined in accordance with the provisions of the Credit Agreement. All unpaid
amounts of principal and interest shall be due and payable in full on the Final
Maturity Date (as defined in the Credit Agreement).

          All payments of principal and interest in respect of this Note shall
be made in lawful money of the United States of America in same day funds at the
office of the Lender located at 801 W. Big Beaver Road, Suite 201, Troy,
Michigan 48084, or at such other place as shall be designated in writing for
such purpose in accordance with the terms of the Credit Agreement. Until
notified of the transfer of this Note, the Borrower shall be entitled to deem
the Lender or such person who has been so identified by the transferor in
writing to the Borrower as the holder of this Note, as the owner and holder of
this Note. Each of the Lender and any subsequent holder of this Note agrees that
before disposing of this Note or any part hereof, it will make a notation hereon
of all principal payments previously made hereunder and of the date to which
interest hereon has been paid on the schedule attached hereto, if any; provided,
                                                                       --------
however, that the failure to make notation of any payment made on this Note
-------
shall not limit or otherwise affect the obligation of the Borrower hereunder
with respect to payments of principal or interest on this Note.

          This Note is referred to in, and is entitled to the benefits and
subject to the terms and conditions of, that certain Credit Agreement dated as
of September 20, 2001 (as amended, modified, renewed or extended from time to
time, the "Credit Agreement") between the Borrower and the Lender. The Credit
           ----------------
Agreement, among other things, (i) provides for the making of a term loan by the
Lender to the Borrower in an aggregate amount not to exceed at any time
outstanding the U.S. dollar amount first above mentioned (the "Loan"), the
                                                               ----
<PAGE>

indebtedness of the Borrower resulting from the Loan being evidenced by this
Note, (ii) contains provisions for acceleration of the maturity hereof upon the
happening of certain stated events and (iii) permits the prepayment of the Loan
by the Borrower prior to maturity.

          The Borrower's obligations under this Note are also secured by all
assets of the Borrower pursuant to the terms of the Credit Agreement and the
Collateral Documents (as defined in the Credit Agreement). The terms and
conditions of the Credit Agreement and the Collateral Documents are incorporated
herein by this reference.

          This Note is subject to conversion into the Common Stock of the
Borrower as further provided in the Credit Agreement.

          The terms of this Note are subject to amendment only in the manner
provided in the Credit Agreement.

          No reference herein to the Credit Agreement or the Collateral
Documents, and no provision of this Note or such agreements shall alter or
impair the obligation of the Borrower, which is absolute and unconditional, to
pay the principal of and interest on this Note at the place, at the respective
times, and in the currency herein prescribed.

          The Borrower promises to pay all reasonable costs and expenses,
including reasonable attorneys' fees, incurred in the collection and enforcement
of this Note. The Borrower hereby consents to renewals and extensions of time at
or after the maturity hereof, without notice, and, subject to the Credit
Agreement, hereby waives diligence, presentment, protest, demand and notice of
every kind and, to the full extent permitted by law, the right to plead any
statute of limitations as a defense to any demand hereunder.

          IN WITNESS WHEREOF, the Borrower has caused this Note to be executed
and delivered by its duly authorized officer, as of the date and the place first
above-written.

                                             AMERIGON INCORPORATED,
                                             a California corporation

                                             By:    /s/ Richard A. Weisbart
                                                 -------------------------------
                                                 Richard A. Weisbart,
                                                 President & CEO

                                       2

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