Wiring Gremlins >:(

[NightRunner]

So I have a problem with my 1991 C1500. I have a short or something that's causing battery drain somewhere. I pulled the engine harness as I had a couple of frayed wires. Repaired them, and put it all back together. Put a fresh battery in, and within a week it's dead again. I also took out the radio and interior lights as well. Headlights and tail lights aren't staying on, so I'm hard pressed to figure out where the problem is. I can't imagine there's much more wiring within this truck, so where should I look next?

 

[df2x4]

I'd put a multimeter on the battery terminals and check for current draw while it's sitting, then pull fuses until it goes away. That'll at least tell you which circuits are causing problems.

 

[NightRunner]

Good call, I've been meaning to get my hands on a multimeter anyways

 

[df2x4]

The fuses in the box should have test points on them as well, so you can just test circuits individually if you have a meter without pulling or disconnecting anything.

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[PlayingWithTBI]

You could also have a draw from the alternator.

 

[SAATR]

In order to check for a current draw with a multimeter, you have to have the meter connected in series with either the power or ground cables of the battery. Simply attaching the meter across the battery terminals or across the test points of a fuse will put the meter in parallel, which will not give an accurate reading, if any at all.

If you want a simple tool to test individual circuits, find a blown fuse (amp rating doesn't matter) and solder some short pieces of solid core copper wire (Romex, like you would use for wiring a house) to the test points on the fuse. That way you have a solid piece to attach alligator clip style leads to, and force all current to flow through the meter. It also means you won't screw up the fuse block trying to shove test leads into the slots.

 

[df2x4]

I completely forgot that connections need to be in series for current draw testing, good call.

 

[PlayingWithTBI]

here's my old standby - I bought them ~25 years ago. IIRC the AMP clamp was ~$100 and the meter was even more.

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