1994 GMC Sierra 1500 is eating batteries

[crabtruck]

Good, you're making progress. Basically a process of dividing the wires
into those that are and are not part of the problem.
Leave the alt connected and re-connect the junction block wire from batt.
There are up to seven other wires connected to that junction block,
mostly in the form of fusible links. Take those off one by one.

Two things to pay attention to:
1) Just because the problem stop when you remove a wire
. . does NOT mean it's a bad guy. If the problem STAYS there,
. . that DOES mean the remove wire was innocent.
2) The problem may dissapear at any time because you are bumping wires.
. . If it dissapears, try jiggling wires to see if it comes back.

Those seven or so links are for the "fuses" inside the cab, fuel and PCM stuff,
AC, aux cooling fans, 4wd stuff, key and some HAZ and ACC stuff,
and possibly an aux Htr/ac if you had it. All depends on how equipt.

Keep playing, they're only wires and walking bites.

BTW: You don't need to quote me in your reply.
If I didn't read it when I wrote it, I'm not goiong to start now.

[BernieB]

Had one of these drive me nuts on my GMC. Every 7-8 days I'd have two dead batteries if I didn't use the truck much. Turned out that the 25 degree slope of my driveway (where the truck is parked) was just enough to make the underhood light come on if the wind rocked the truck a little bit. I saw it flickering one night when I walked down the driveway to get the mail out of the box and thought I had a fire under the hood.

[RollTidenIA]

Crabtruck:
Thanks for the help! I'll keep chasing tonight. While I had everything disconnected last night, I touched each individual wire from the junction block to the batt lead separately and every one of them would cause the draw to jump through the roof. That was with the Alt. disconnected. Does that make any sense? Is there a loop from the junction block back to the alternator somewhere that I'm missing? Not sure why the Alt. is causing the draw as well.

I'll also have to swap my battery out - put it on the charger overnight, but it wouldn't start the truck this morning. Oh well, it's still within the 18 month 'free replacement' range, so I'll claim it's a 'dud'.

Bernie:
That would tick me off. Something so simple, yet so destructive. ha! I've checked all of the 'courtesy' lights I can find - no light installed in glovebox, removed bulb from cab overhead light, no light installed under hood. Oh well... Just keep chasing I guess..

[crabtruck]

Do I understand this correctly ?
Alt is disconnected + junction block disconnected = no draw.
Alt is disconnected + any one(1) fusible link hooked = 200 draw.

Are you touching fusible link leads to batt wire in free air or on block?
Did you take out hood bulb or is there no socket ? Socket may be source,
and I think its pigtail connects at junction block too.
Get as much seperation of things as you can.

Make sure the batt feed insulation is not partly rubbed through,
which might make it draw as you drag to test connections with link.

Stop that battery-killing by disconnecting if parking until you get a fix.

[RollTidenIA]

OK.. I finally have it narrowed down to a single electrical system - the brakes.

I stopped and got a $3 test light to use along with the multimeter. Great idea! Quick and easy to test voltage in different areas.

I opened up the junction block in the engine compartment again. With the neg batt terminal disconnected, I put the test light in-line with the neg bat terminal and a nearby ground. I began testing each individual wire in the junction block until I narrowed it down to a single wire. With only that wire connected to the juncion block, I began pulling fuses one at a time. Pulled the brake fuse and the light went out. Jackpot.

I unplugged the wiring harness from the brake pedal switch but the light still stayed on. So there must be a short somewhere between the junction block and the wiring harness going to the brake pedal switch itself.

At least I have it narrowed down to a single system to chase down.

[crabtruck]

Good work !
Brake fuse supplies the TCC/Stoplamp Sw(pedal), the VSS buffer and the antilock as "brand name" items.
It also supplies the audio alarm mod and HAZ flashers.

You checked the pedal, so next would be
unplugging the ABS under the hood
and the HAZ flasher as the easiest checks.
Then audio alarm mod - it's in the conv cntr
and chimes key-in,seatbelt off, etc.
VSS buffer is more of a pain to reach.

[gmctrucks]

This is one good write up and all you guys have had good answers. Plus I learned very much and RollTidenIA has been coming back to let us all know what's going on so we can all learn which is super.

[RollTidenIA]

Well, I thought I was going down the right path, but I'm running out of roads to go down.

The actual fuse that makes the infamous 'test light' go out is the 'STOP' fuse - I *assume* that is for the brake lights, etc.

So far I have pulled the Hazards flasher relay, turn signal relay, chime noise maker, unplugged both rear brake light assemblies and checked the brake assembly on back of the cab.. Still can't locate exactly where the draw is coming from.

There isn't ABS to worry about on this one.

What and where is the VSS buffer you are referring to?

EDIT: I googled the VSS buffer and found it behind the glove box. While I had that opened up, I unplugged all of the relays behind the glove box one at a time - still no good.

I'm running out of ideas...

[gmctrucks]

How about that plug that one can place on the OEM wiring harness to hook up some trailer lights? I know many of people have had problems there.

[RollTidenIA]

Originally Posted by gmctrucks

How about that plug that one can place on the OEM wiring harness to hook up some trailer lights? I know many of people have had problems there.

Unplugged that as well, but forgot to mention it in my earlier post.

Do the brake lights have a relay somewhere? If so, would it be one of the relays that I unplugged behind the glove box? If so, with the problem still existing with the relay unplugged, would it make sense that the short is occurring between the fuse and the relay? Of course, this is assuming that it is the brake lights and not something else running on the 'stop' fuse.