<PAGE>   1

                                                                     Exhibit 4.3



                          FORM OF SUBSCRIPTION WARRANT

                                    WESTCORP
                    SUBSCRIPTION WARRANT FOR RIGHTS OFFERING
                    FOR HOLDERS OF RECORD ON MARCH __, 2001


----------------------------                        ----------------------------
SUBSCRIPTION WARRANT NUMBER                                         CUSIP NUMBER

----------------------------   -------------------  ----------------------------
SHARES ELIGIBLE TO SUBSCRIBE         RIGHTS                   RECORD DATE SHARES


          Westcorp (the "Company") is conducting a rights offering (the "Rights
Offering") which entitles the holders of shares of the Company's common stock
(the "Common Stock"), as of the close of business on March __, 2001 (the
"Record Date") to receive one transferable right (each, a "Right") for each
share of Common Stock held of record on the Record Date. Holders of Rights are
entitled to subscribe for and purchase one share of Common Stock for every ___
Rights (the "Basic Subscription Right") at a subscription price of $____ per
share. If any shares of Common Stock are not purchased by holders of Rights
pursuant to the Basic Subscription Right (the "Excess Shares"), any holder
purchasing all of the shares of Common Stock available to that holder may
purchase an additional number of the Excess Shares, if so specified in the
subscription documents, subject to proration. No fractional shares or cash in
lieu thereof will be issued or paid. Set forth above is the number of shares of
Common Stock held by such holder, and the number of whole shares to which each
holder is entitled to subscribe pursuant to the Basic Subscription Right
(rounded down, if applicable, to the nearest whole share).

          For a more complete description of the terms and conditions of the
Rights Offering, please refer to the Prospectus dated March __, 2001 (the
"Prospectus"), which is incorporated herein by reference. Copies of the
Prospectus are available upon request from Mellon Investor Services LLC
(toll free (866) 825-8874).

          This Subscription Warrant (or a Notice of Guaranteed Delivery) must be
received by Mellon Investor Services LLC together with payment in
full of the subscription price by 5:00 p.m. New York City time, on April __,
2001 (unless extended in the sole discretion of the Company) (as it may be
extended, the "Expiration Date"). Any Rights not exercised prior to the
Expiration Date will be null and void. Any subscription for shares of Common
Stock in the Rights Offering made hereby is irrevocable.

          The Rights represented by this Subscription Warrant may be exercised
by duly completing Form 1; may be transferred, assigned, exercised or sold
through a bank or broker by duly completing Form 2; and may be sold through
Mellon Investor Services LLC by duly completing Form 3. Each of
these forms is set forth on the reverse hereof. Rights holders are

<PAGE>   2

advised to review the Prospectus and instructions, copies of which are available
from Mellon Investor Services LLC, before exercising or selling
their Rights.

SUBSCRIPTION PRICE:  $_____ PER SHARE

          The registered owner whose name is inscribed hereon, or its assigns,
is entitled to subscribe for shares of Common Stock of the Company upon the
terms and subject to the conditions set forth in the Prospectus and the
instructions relating to the use hereof.

          The Subscription Warrant is transferable, and may be combined or
divided at the office of Mellon Investor Services LLC If the number
of transferred Rights would otherwise allow the purchase of a fractional share,
the number of shares which may be purchased must be rounded down to the nearest
whole share (or any lesser number of whole shares) that may be purchased with
that number of Rights.

          Rights holders should be aware that if they choose to exercise or
transfer only part of their Rights, they may not receive a new Subscription
Warrant in sufficient time to exercise the remaining Rights evidenced thereby.

                  FORM 1 (on reverse of Subscription Warrant)

EXERCISE AND SUBSCRIPTION: The undersigned hereby irrevocably exercises one or
more Rights to subscribe for shares of Common Stock as indicated below, on the
terms and subject to the conditions specified in the Prospectus, receipt of
which is hereby acknowledged.

(a) Number of whole shares subscribed for pursuant to the Basic Subscription
Right ____ X $_____ = $_____ payment. (___ Rights needed to subscribe for one
share.)

(b) Number of whole shares subscribed for pursuant to the Oversubscription Right
____ X $_____ = $_____ payment.

(c) Total Subscription (sum of payment amounts on lines (a) and (b)) = $________
payment.*

METHOD OF PAYMENT (CHECK AND COMPLETE APPROPRIATE BOX(ES)):

     [ ]  Check, bank draft, or U.S. postal money order payable to "Mellon
Investor Services LLC, as Subscription Agent" or

     [ ] Wire transfer directed to The Chase Manhattan Bank, New York, NY, ABA
No. 021000021, Mellon Investor Services, LLC, MISC Reorg. Control A/C 323-885489
-(Westcorp).

(d) If the Rights being exercised pursuant to the Basic Subscription Right do
not constitute all

<PAGE>   3

of the Rights represented by the Subscription Warrants (check only one):

     [ ] Deliver to the undersigned a new Subscription Warrant evidencing the
remaining Rights to which the undersigned is entitled.

     [ ] Deliver a new Subscription Warrant in accordance with the undersigned's
Form 2 instructions (which include any required signature guarantees).

     [ ] Sell the remaining unexercised Rights in accordance with the
undersigned's Form 3 instructions.

     [ ] Do not deliver any new Subscription Warrants to me.

(e)  [ ] Check here if Rights are being exercised pursuant to the Notice of
Guaranteed Delivery delivered to the Subscription Agent prior to the date hereof
and complete the following:

       Name(s) of Registered Holder(s) ____________________________________
       Window Ticket Number (if any) ______________________________________
       Date of Execution of Notice of Guaranteed Delivery _________________
       Name of Institution Which Guaranteed Delivery ______________________

* If the aggregate Subscription Price enclosed or transmitted is insufficient to
purchase the total number of shares included in lines (a) and (b), or if the
number of shares being subscribed for is not specified, the Rights holder
exercising this Subscription Warrant shall be deemed to have subscribed for the
maximum amount of shares that could be subscribed for upon payment of such
amount. If the number of shares to be subscribed for pursuant to the
Oversubscription Right is not specified and the amount enclosed or transmitted
exceeds in aggregate the Subscription Price for all shares represented by this
Subscription Warrant (the "Subscription Excess"), the Rights holder exercising
this Subscription Warrant shall be deemed to have exercised the Oversubscription
Right to purchase, to the extent available, that number of whole shares of
Common Stock equal to the quotient obtained by dividing the Subscription Excess
by the Subscription Price, subject to proration as described in the Prospectus.
To the extent any portion of the aggregate Subscription Price enclosed or
transmitted remains after the foregoing procedures, such funds shall be mailed
to the subscriber without interest or deduction as soon as practicable.

Subscriber's Signature __________________  Telephone No.  (___)________________


                   FORM 2 (on reverse of Subscription Warrant)

<PAGE>   4

TO TRANSFER YOUR SUBSCRIPTION WARRANT OR SOME OR ALL OF YOUR RIGHTS, OR TO
EXERCISE OR SELL RIGHTS THROUGH YOUR BANK OR BROKER: For value received, Rights
represented by this Subscription Warrant are hereby assigned to (please print in
full name and address and Taxpayer Identification Number or Social Security
Number of transferee):

Name: _______________________________________________________________

Address: ____________________________________________________________

_____________________________________________________________________
Signature(s) of Transferee(s)

Signatures Guaranteed by: ___________________________________________

Proceeds from the sale of Rights may be subject to withholding of U.S. taxes
unless the Seller's certified U.S. taxpayer identification number (or
certificate regarding foreign status) is on file with the Subscription Agent and
the seller is not otherwise subject to U.S. backup withholding.


                  FORM 3 (on reverse of Subscription Warrant)

TO SELL SOME OR ALL OF YOUR UNEXERCISED RIGHTS THROUGH THE
SUBSCRIPTION AGENT:

The undersigned hereby authorizes the Subscription Agent to sell _______________
Rights represented by this Subscription Warrant but not exercised hereby and to
deliver to the undersigned a check for the proceeds, if any, from the sale
thereof, less any applicable brokerage commissions, taxes or other direct
expenses of sale. The Subscription Agent's obligation to execute orders is
subject to its ability to find buyers for the Rights.

______________________________________________________________
Subscriber's Signature

In order to sell Rights through the Subscription Agent, you must complete and
sign the substitute Form W-9 as provided in Section 8 of the instructions.


                   FORM 4 (on reverse of Subscription Warrant)

DELIVERY INSTRUCTIONS: Address for mailing of stock or new Subscription Warrant
or any cash payment in accordance with the Prospectus, if different from the
address shown on the face of this Subscription Warrant:

Name: _________________________________________________________________

Address: ______________________________________________________________