Issue: Battery Drains Overnight (0.78A Draw)

Hey everyone,

I’m trying to track down a parasitic battery drain on my 1999 Ford Ranger 4WD 3.0L V6 FFV OHV. My battery keeps dying overnight, so I tested for excessive current draw and found a 0.78-amp drain when the truck is off, which is way too high.

What I Tested So Far:

I used a multimeter in series on the negative battery terminal and started pulling fuses. Here’s what I found:

1. In-Cab Fuse Box:

• Pulled Fuse #25 (7.5A – GEM Module) → The drain dropped to 0.02A
• Pulled Fuse #26 (7.5A – Instrument Cluster/PCM) → The drain dropped to 0.18A

2. Under-Hood Fuse Box:

• Pulled Fuse #1 (50A – Alternator Circuit) → The drain dropped to 0.01A

My Questions & Next Steps:

1. Does this confirm my alternator has a bad diode? (Since pulling Fuse #1 nearly eliminated the drain?)
2. What could be staying on in the GEM circuit? (I don’t have power locks/windows or factory keyless entry, but could an aftermarket alarm be causing the drain?)
3. Could my PCM be staying awake and causing part of the drain? (Since pulling Fuse #26 dropped the draw but didn’t eliminate it completely.)
4. What should I do next? I haven’t tested unplugging lights, relays, or other accessories yet—what’s the best way to go about that?
5. Could my blinking "Theft" light on the dashboard be related? (I’ve never seen or heard an alarm go off, but the light blinks when the truck is off.)
6. I have a strange issue where my key can be pulled out of the ignition while the engine is running—not sure if that’s related, but mentioning it just in case.

Extra Info:

• No known aftermarket accessories, but I bought the truck used, so there may be something hidden.
• Dome light turns off properly, no stuck door ajar light.
• Overnight, I pull Fuse #25 in hopes my battery doesn’t die.
• Truck runs fine otherwise, just the battery dies when parked.

If anyone has dealt with a similar issue or has suggestions on what to check next, I’d really appreciate the help! Thanks in advance!