<PAGE>   1
                                                                   EXHIBIT 10.36

                              REVOLVING CREDIT NOTE



$1,000,000
Due Date: The earlier of Demand
or December 31, 2000                                   Dated:  December 30, 1999


         FOR VALUE RECEIVED, the undersigned promises to pay to the order of
WILLIAM P. O'REILLY (the "Lender"), at his office at 2000 Town Center, Suite
690, Southfield, Michigan 48075, or at such other place as Lender may designate
in writing, the principal sum of One Million ($1,000,000) Dollars, or such
lesser sum as shall have been advanced by Lender to Borrower pursuant to that
certain Loan and Security Agreement dated as of December 30, 1999, between
Borrower and Lender (which, together with all amendments and modifications
thereof, is hereinafter referred to as the "Loan Agreement"), plus interest as
hereinafter provided, all in lawful money of the United States of America, in
accordance with the terms hereof.

         The unpaid principal balance of this Revolving Credit Note ("Note")
shall bear interest computed upon the basis of a year of 360 days for the actual
number of days elapsed in a month, at a rate of interest (the "Effective Rate")
which is equal to the prime rate as reported in The Wall Street Journal, plus
1.5% per annum.

         Interest on all principal amounts advanced by Lender from time to time
and unpaid by Borrower shall be paid on the last day of the month hereafter and
on the last day of each month thereafter until the Due Date, upon which date the
entire unpaid principal balance of this Note, together with all accrued and
unpaid interest, shall be due and payable in full. If Borrower makes and Lender
accepts a payment made five (5) days after the last day for such payment,
Borrower shall pay with such payment a late charge equal to five (5%) percent
thereof. Payments required on the Due Date shall not have a late charge, but the
default interest specified below shall accrue commencing on the day following
the Due Date.

         Advances of principal, repayment, and readvances may be made under this
Note from time to time, upon the terms set forth in the Loan Agreement and said
Loan Agreement is 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. Lender
shall furnish Borrower with a monthly 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 thirty (30) days after such statement has been furnished. Borrower
expressly assumes all risks of loss or delay in the delivery of any payments

<PAGE>   2

made by mail, and no course of conduct or dealing shall affect Borrower's
assumption of these risks.

         Upon the Due Date, which Borrower acknowledges may be upon demand,
Lender, without prior notice to Borrower, may declare the entire unpaid
principal balance of this Note and all accrued interest, together with all other
indebtedness of Borrower to Lender, to be immediately due and payable. Upon the
occurrence of any Default specified on the Loan Agreement or upon demand, the
unpaid principal balance of this Note shall bear interest at a rate which is
three (3.0%) percentage points greater than the Effective Rate. After Default or
demand, Lender may apply its own indebtedness or liability to Borrower to any
indebtedness due under this Note. Borrower agrees to pay all of the Lender's
costs incurred in the collection of this Note as provided in the Loan Agreement.

         Acceptance by Lender of any payment in an amount less than the amount
then due shall be deemed an acceptance on account only. Upon any Default,
neither the failure of the 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 the Lender to demand strict performance of
any other obligation of the 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 the Borrower or any
other person who may be liable hereunder.

         Borrower acknowledges that no Default is necessary for Lender to make
demand.

         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, and to the release of
any collateral or any part thereof, with or without substitution. The liability
of Borrower under this Note shall be absolute and unconditional, without regard
to the liability of any other party. This Note has been executed in the State of
Georgia, and all rights and obligations hereunder shall be governed by the laws
of such state.

         In no event whatsoever shall the interest rate and other charges
charged hereunder exceed the highest rate permissible under any law which a
court of competent jurisdiction shall, in the final determination, deem
applicable hereto. In the event that a court determines that Lender has received
interest or other charges hereunder in excess of the highest rate applicable
hereto, Lender shall, either in its sole discretion, promptly apply such amounts
to the principal due hereunder or refund such amount to Borrower and the
provisions herein shall be deemed amended to provide for such permissible rate.

         Lender acknowledges that the Borrower's obligations under this Note are
limited by the terms of the Senior Indebtedness and Senior Lien (as defined in
the Loan Agreement)


                                     - 2 -

<PAGE>   3

         This Note is issued pursuant to the terms of the Loan Agreement and is
secured by the Collateral, as defined in the Loan Agreement. All of the terms,
covenants and conditions of the Loan Agreement are hereby made a part of this
Note and are hereby incorporated by reference.

                                           "BORROWER"

                                           ELTRAX SYSTEMS, INC.,
                                           a Minnesota corporation


                                           By:    /s/ Don G. Hallacy
                                              ----------------------------------
                                                  Don G. Hallacy, President





                                     - 3 -