Hello! I've been having a power drain in my '96 1500 (318/auto) since I bought it nearly two years ago. It was a daily driver for most of that time, but I now have a car (longer drive to work, needed better mpg). If the truck sits for more the three days, I have to boost it. A new battery didn't fix it (though the old one was shot), I had the alternator tested, and was told it was bad. I had a second one off a a 360 I'm one day building for it that is good, didn't help. So there's something drawing power that isn't supposed to. The other day I noticed that when I shut the truck off, the fuel gauge doesn't go to empty, just stays wherever the fuel level is. The gauge works fine, just doesn't seem to shut off. Would that drain the battery enough to cause it to not start after three days? I checked the wiring where I can get to it, and I didn't find any breaks/melted wires. I'm thinking then the issue is in the sending unit?

 

The Fuel gauge on our trucks are different than other vehicles I've seen. Mine is a 94 and when you shut it off, it just stays where it reads. If you go to fill up on a low tank, and then start it up after filling, you will see that garage slowly go back up. It's unlike my Chevy where that thing bounces going up And down the highway. The guage isn't your concern. I'd start searching for other things.

 

Plus the gauges are controlled by the pcm. You need to trace what's draining the battery. Put digital vom on the battery and start pulling fuses.

 

Bah, thought I had it! Oh well. Next nice day I'll go through it. What kind of draw would be normal?

 

I believe that there is a spec for the drain in the service manual. Pull the IOD (ignition off drain) fuse, see what happens. The drain should be in the milliamp range though. Aftermarket stereo? Some of those will drain a lot, even off.

 

I did put a Sony CD/Bluetooth player in it, but it was going dead before that. I haven't checked it out yet, it's been snowing/raining the last few days, hopefully soon!

 

Finally got time to check this out. With the IOD fuse pulled, it read .026. I pulled every fuse one at a time, the only one that did anything was the 40a stop/head light fuse under the hood. With that pulled, the meter dropped to 0. There is a hidden hitch, with both a factory trailer light plug and one added on. All the trucks lights work fine, so I'll dig into the added plug and start there.
I also borrowed a battery tester, that could load test the alternator. It stays dead on 14v while idling, with a load on, it drops to 12.2 and stays there. Shouldn't it stay around 14v?

 

What kind of load? Normal stuff and a relatively good battery, yes, it should stay up there. A dead battery will pull it down quite a bit.

Stop/head fuse is interesting. Keep the fuse in and pull the headlight switch off of the wiring harness. But, it may be some of your tow wiring is shorted, possibly even within the socket (dirt, debris, water). You could also leave the fuse in and disconnect your brake light switch, at the pedal.

 

The battery is new, and when it's fully charged, the battery tester says it's good. I don't know how much of a load it puts on, it's just a plain load tester. I found out today that my multimeter is junk. When the load tester is on with the truck running, it shows under 14v, while if I put the multimeter on it at the same time, it reads over 18v, and told me yesterday it was at 14v even. If I take it off and put it back on, it'll give me a completely different number. Great. I'll trust the load tester for now I guess.
I did find that the added flat style trailer light harness was completely full of corrosion and junk, so I cut it off and taped off the wires for now. I'll let it sit for a few days and see what happens.
i also changed out the IAC sensor and cleaned up the tb. I have a TP sensor as well that came with a 52mm FastMan tb, but it's wire connection isn't the same. It seems to run better and no random stalling after starting!

 

So the trailer harness seems to have been the culprit. Thanks for the help!