gem module, lincoln navigator, rear wheel drive

I have a 1999 lincoln navigator. I need a new gem module but lincoln wants $800 for it. Will any other module interchange with the lincoln one or is it specific to each vehicle. I've found a couple of ford modules but don't know if they will work. Any help would be greatly appreciated.

Answer
    This is Ford's name for the Body Control Computer.  RockAuto has rebuilt ones for sale that fit your vehicle.  They are made by A1 Cardone in Philly (a very reputable company) and cost about $170 with the exchange of the old one.  Part number 73-3019 fits the four wheel drive, and # 73-3022 fits the rear wheel drive.  You can probably get one at a local parts store, as well, but you will pay more money.  Not $800, though.
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