Hi There. I have a 2000 F350 with the 7.3. Recently my batteries have been draining overnight. I load tested both batteries already. Both read good with the load and battery test. Tested for charging. Everything reads good with the charging system. Today I unhooked the negative terminals from each battery to test for draw. When running my test light from the post to the ground cable the test light is on bright. Therefor confirming a draw. I pulled all fuses under hood and no change in the light. I went into the cab and started pulling fuses. When I got to fuse 4 (glove box lamp, map lamps, power mirrors, and underhood lamps) the light dimmed slightly. I kept going and when i got to fuse 14 (dome lamp, cargo lamp, courtesy lamps, running board lamps) i pulled that fuse and it seemed that Relay 1 (interior lamp relay) started making noise. Not sure if that is normal? I replaced that relay and still makes minor noise. Next I pulled fuse 15 (stop lamp switch, GEM, PCM, 4WABS module, brake shift interlock, cluster and pcm keep alive memory) and when i pulled that fuse the light went completely off. I am so lost right now at where to start knowing both fuses were causing a draw. Any help would be great!!!!!

And I do not know if this would have anything to do with it but my wipers come on, on there own randomly and when i actually do turn them on, they only work right on the faster settings, the lower settings it goes about 1/3rd the way up the windshield and then stops and then couple seconds later continues and then stops and then eventually it will go the full cycle. Sorry for the essay i wrote i just didnt want to miss anything.

 

Sounds like maybe you have a light that isn't turning off?

 

Maybe a light, but it should be obvious if one were still burning after the built-in delay. Hmmm, speaking of that, maybe a failing GEM? I would expect fuse 15 to have some draw for the keep alive memory, but if the GEM is failing (short?) then that might explain the extra draw.

 

It doesn't look to me like any lights are staying on after the delay. Is there a test to verify a failing GEM?

 

The GEM (General Electronics Module) controls many minor circuits (lamps, lights, etc.) in the cab. I'm not sure if there is a t-shoot procedures for it (might try searching this forum). I did see a post earlier that had a link to an easy to follow battery drain test Ford Truck Enthusiasts Forums - View Single Post - F250 V10 2006 Battery Discharge
that you might try to make sure you've got the right problem circuit.

 

Question: Is the big issue the fact that it wont start in the morning due to the drained batteries? How are you starting it? Jump/Charge? Reason I ask, is years ago, I had a 99 7.3 and had a similar issue to yours, where I thought the batteries were dying overnight, and it would only start after a jump/charge. Checked batteries and Alternator, but all checked out good. It turned out to be my starter. It would start when warm or on FULL charge, but after sitting overnight the voltage drop was enough that the starter wouldnt turn hard enough. I chased this for a good month, so if I were you, even though you might not think it's the problem, go get your starter checked.

Oh, and by the way, when you get the starter checked, it might test "good", but I would ask them to test a new one in front of you as well. You will be able to tell the difference. This is what I needed to do, as the starter seemed ok with no load, but compared to a new one, it was night and day.