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I have had a slight battery drain on my Ford Ranger, enough to kill the battery after a few days of sitting. The battery is new.

This is the troubleshooting I have done so far:

  1. Tested the battery unplugged at 12.67 volts. Tested the battery running at 13.7-14.3 volts.

  2. Tested the amp draw resting at 0.27 amps. After 40 minutes this drops to 0.10 amps with the doors shut.

  3. Tested the amp draw with the door opened but latch pressed in to simulate a closed door. Similarly at 0.27 amps until it drops again to 0.15 amps.

  4. Removed fuse 26 with door open - dropped from ~3.8 amps to 0.15 amps (my guess is this controls the dome light)

  5. Removed fuse 25 with door open - dropped from ~3.8 amps to 0.02 amps.

  6. Repeated step 5 with the door simulated closed and after waiting for the drop for 40 minutes. Also dropped to 0.02 amps after removing 25. Before 25 was removed, 26 was removed with no effect (stayed at 0.15 amps)

I have concluded that fuse 26 is of no concern, since the simulated closed door at best gets 0.15 amps, and the result of it dropping with the door open is because of the dome light.

Fuse 25, according to this website controls the GEM and the speedometer.

My question is, what is the next best step to diagnosing the draw? My plan is to find all the components the GEM controls and attempt at unplugging them with the simulated door closed scenario, and seeing which kills the draw. Is this correct, or am I barking up the wrong tree?

The truck also has an aftermarket alarm system, which I have been wanting to uninstall for sometime. Is it possible this is routed through the GEM?

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    I think this is an excellent first question, welcome to the site.
    – Zshoulders
    Commented Dec 12, 2016 at 17:38
  • What engine do you have? 4WD or 2WD? Regular cab or extended?
    – Ben
    Commented Dec 13, 2016 at 0:03
  • Can you figure out which fuse protects the alarm circuit? If it is 25 or one of the other GEM related fuses it might be worth starting with the alarm. Also, in terms of picking circuits to test, the most obvious ones are those that have wires that might get damaged (e.g., door circuits).
    – dlu
    Commented Dec 23, 2016 at 4:20

2 Answers 2

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So after looking up what a GEM was (its the Ford name for the thing that controls the majority of the interior and some of the exterior electronics, if anybody else was wondering), A reasonable first guess is the aftermarket alarm. Aftermarket electronics are rarely designed in a way that is electrically sound, and even more rarely installed correctly. From personal experience, for almost any electrical problem, I would absolutely start there.

If that isn't the problem, you'd need to go through everything that connects to the GEM, just like you said. I have not been able to find a definitive list of what that entails. You may be able to make some educated guesses (burned out dome lights, seatbelt beeper doesn't beep anymore, any non-functioning electronic, etc.) Its also worth noting that, per your source, fuse 28 is also GEM. edit: and fuses 10 & 20

From reading on a few different Ford forums, it seems as though the GEM getting wet is an issue for certain years/models, although I haven't found mention of the Ranger. Still might be worth a look; its hard to tell from the photos if you can get at it easily or not.

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Fuse 25 powers the GEM, Instrument Cluster and the Passive Anti-Theft systems.

You are correct, your best bet would be to unplug these one by one and figure out which one is causing the draw. An alternative would be to find the splice and do the work from there. Another thing to consider before you replace any parts is whether the modules are being kept awake externally.

As to the aftermarket alarm it could be, but it hard to say without seeing how the alarm system was installed. Likely not though.

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