2000 Ford Mustang parasitic draw

i have a parasitic draw that is effecting my battery. i tested the fuses and one has 2.8 mil volts with the ignition switch off and 30 minutes of sleep. the fuse is for the GEM module. this seems to be the issue. how can i determine which component on this fuse is the problem? could the electric draw be some other problem?

2.8 mV across the fuse terminals after 30 seconds with the fuse IN I assume? Not sure how big the GEM fuse is… Fuse #39 is the GEM fuse, I think and that’s 5 amps? - that’s a 177 mA draw Too much draw by about 6 times but not really all that large a draw.

Does this car sit a lot? Do you have any aftermarket accesories like and alarm, remote start or big stereo amps? I’d look there.

The GEM controls a lot of stuff, communication line, power window controls, door switches, brake switch, ign key warning switch, seat belt switches… a bunch. But this thing is a control module and not a power distribution center. 5 amps won’t drive much.

I suggest checking the fuses for each of the items the GEM controls to find a bigger drain. If you don’t find one, the GEM s the likely problem - and they are problems on Fords.

I was able to perform a AMP test using the meter in-line with the negative terminal on the battery (disconnected) and found that the #6 fuse under the hood (40amp instrument panel, PCM) had .24 amps draw. After removing this fuse the draw was zero. However, I also removed the two other fuses, separately one at a time, and the draw went down to .10 amps for fuse #39 (5amp GEM) and .13 amps for fuse #27 (25amp Radio). Is the fuse #6 under the hood somehow connected to systems related to the other two fuses? How can I determine what the problem is? This is so frustrating.

Yes, the car does sit, mostly in the winter. Mustang does not drive well in the bad weather. No aftermarket accessories. However, it did have halogen lights that I removed a few years ago. I took out all the wiring and ballasts.

If it is the GEM, can I just replace it with a new one? Or is there some programming or setup required?

Thanks for your help!

You have to wait an hour to make sure all computers/modules go to sleep prior to doing a parasitic draw test.


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I understand the GEM needs to be a match for your vehicle. The interwebs are unclear if it needs to be programmed. A used replacement, probably not, a new Ford unit, maybe. I also understand that they are not available from Ford but I see some are available from the aftermarket.

Your first post mentioned millivolt readings, not amps so I thought you were measuring across each fuse for voltage drop. That is a good way to determine parasitic draw with everything connected and powered down for an hour to make sure everything goes to “sleep” If you have to keep a door open to reach the fuse panel, tape the door switch down so the car thinks it is closed up or the GEM will stay awake.

This site has charts for the voltage drops across various fuse sizes minis, maxis, ect.