<PAGE>   1
                                                                   EXHIBIT 10.4

                      SECOND AMENDED DEMAND PROMISSORY NOTE


$50,000,000.00                                                 DETROIT, MICHIGAN
                                                  DATED: AS OF DECEMBER 13, 1999

         FOR VALUE RECEIVED, BINGHAM FINANCIAL SERVICES CORPORATION, a Michigan
corporation ("Borrower"), promises to pay ON DEMAND to the order of Sun
Communities Operating Limited Partnership, a Michigan limited partnership
("Lender"), at 31700 Middlebelt Road, Suite 145, Farmington Hills, Michigan
48334, or at such other place as Lender may designate in writing, the principal
sum of FIFTY MILLION AND NO/100 DOLLARS ($50,000,000.00) or such lesser sum as
shall have been advanced by Lender to Borrower under the loan account
hereinafter described, plus interest as hereinafter provided, all in lawful
money of the United States of America, in accordance with the terms hereof. This
Note is subject to the terms of that certain Loan Agreement between Borrower and
Lender dated March 1, 1998, as amended by that certain First Amendment to Loan
Agreement dated as of June 11, 1999 (the "Agreement"), the terms of which are
incorporated herein by reference.

         All advances made hereunder shall be charged to a loan account in
Borrower's name on Lender's books, and Lender shall debit to such account the
amount of each advance made to, and credit to such account the amount of each
repayment made by Borrower. From time to time but not less than quarterly,
Lender shall furnish Borrower a statement of Borrower's loan account, which
statement shall be deemed to be correct, accepted by, and binding upon Borrower,
unless Lender receives a written statement of exceptions from Borrower within
ten (10) days after such statement has been furnished.

         The unpaid principal balance of this promissory note ("Note") shall
bear interest, computed at a rate equal to "LIBOR" as quoted by the Dow Jones
Telerate System "LIBO Page" report of such interest rates as determined by
Reuter's News Service, or (in the sole discretion of the Lender) as quoted in
the Wall Street Journal, as of one business day before the date of this Note,
plus two hundred thirty-five (235) basis points (the "Rate") (which Rate shall
be adjusted for purposes of this Note every six (6) months from the date hereof
to be equal to "LIBOR" as quoted by the Dow Jones Telerate System "LIBO Page"
report of such interest rates as determined by Reuter's News Service, or (in the
sole discretion of the Holder) as quoted in the Wall Street Journal, as of the
business day preceding the date of such adjustment, plus two hundred thirty-five
(235) basis points), in lawful money of the United States of America, in the
manner provided below. On demand, the entire unpaid principal balance of this
Note, together with all accrued and unpaid interest, shall be due and payable in
full within ten (10) days after the date of the demand.

         Advances of principal, repayment and readvances may be made under this
Note from time to time but Lender, in its sole discretion, may refuse to make
advances or readvances hereunder for any reason whatsoever. All payments
received hereunder shall, at the option of Lender, first be applied against
accrued and unpaid interest and the balance against principal. Borrower
expressly assumes
                                     -1-

<PAGE>   2




all risks of loss or delay in the delivery of any payments made by mail, and no
course of conduct or dealing shall affect Borrower's assumption of these risks.

         Upon the occurrence of an Event of Default, as defined in the
Agreement, the entire unpaid principal balance and all accrued and unpaid
interest owing under this Note shall be immediately due and payable, together
with costs and attorneys fees reasonably incurred by Lender in collecting or
enforcing payment. Borrower acknowledges and agrees that the Lender has the
right to demand repayment of the entire balance of this Note, in its sole and
absolute discretion, whether or not an Event of Default has occurred.

         Upon the occurrence and during the continuance of an Event of Default
under this Note, the outstanding principal amount hereof shall bear interest at
a rate which is three percent (3.0%) per annum greater than the Rate otherwise
applicable.

         Acceptance by Lender of any payment in an amount less than the amount
then due shall be deemed an acceptance on account only, and Borrower's failure
to pay the entire amount then due shall be and continue to be a default. Upon
the occurrence of any Event of Default, neither the failure of Lender promptly
to exercise its right to declare the outstanding principal and accrued unpaid
interest hereunder to be immediately due and payable, nor the failure of Lender
to demand strict performance of any other obligation of Borrower or any other
person who may be liable hereunder, shall constitute a waiver of any such
rights, nor a waiver of such rights in connection with any future default on the
part of Borrower or any other person who may be liable hereunder.

         Borrower and all endorsees, sureties and guarantors hereof hereby
jointly and severally waive presentment for payment, demand, notice of
non-payment, notice of protest or protest of this Note, and Lender diligence in
collection or bringing suit, and do hereby consent to any and all extensions of
time, renewals, waivers or modifications as may be granted by Lender with
respect to payment or any other provisions of this Note. The liability of
Borrower under this Note shall be absolute and unconditional, without regard to
the liability of any other party.

         Notwithstanding anything herein to the contrary, in no event shall
Borrower be required to pay a rate of interest in excess of the Maximum Rate.
The term "Maximum Rate" shall mean the maximum non-usurious rate of interest
that Lender is allowed to contract for, charge, take, reserve or receive under
the applicable laws of any applicable state or of the United States of America
(whichever from time to time permits the highest rate for the use, forbearance
or detention of money) after taking into account, to the extent required by
applicable law, any and all relevant payments or charges hereunder, or under any
other document or instrument executed and delivered in connection herewith and
the indebtedness evidenced hereby.

         In the event Lender ever receives, as interest, any amount in excess of
the Maximum Rate, such amount as would be excessive interest shall be deemed a
partial prepayment of principal, and, if the principal hereof is paid in full,
any remaining excess shall be returned to Borrower. In determining whether or
not the interest paid or payable, under any specified contingency, exceeds the

                                      -2-

<PAGE>   3



Maximum Rate, Borrower and Lender shall, to the maximum extent permitted by law,
(a) characterize any non-principal payment as an expense, fee, or premium rather
than as interest; (b) exclude voluntary prepayments and the effects thereof; and
(c) amortize, prorate, allocate and spread the total amount of interest through
the entire contemplated term of such indebtedness until payment in full of the
principal (including the period of any extension or renewal thereof) so that the
interest on account of such indebtedness shall not exceed the Maximum Rate.

         This Note shall be binding upon Borrower and its successors and
assigns, and the benefits hereof shall inure to Lender and its successors and
assigns. This Note has been executed in the State of Michigan, and all rights
and obligations hereunder shall be governed by the laws of the State of
Michigan.

         This Note is an amendment to and restatement of that certain Demand
Promissory Note dated March 1, 1998 and to that certain Amended Demand
Promissory Note dated June 11, 1999 executed by Borrower in favor of Lender (the
"Prior Notes") and this Note amends, supersedes and replaces the Prior Notes.


                                       BORROWER:
                                       BINGHAM FINANCIAL SERVICES
                                       CORPORATION, a Michigan corporation



                                       By: /s/ Ronald A. Klein
                                          --------------------------------------
                                       Its:  CEO
                                          --------------------------------------















                                      -3-