Ways to track down what is sucking my battery dry?

[Ben_Greenberg]

Hey guys,
My 78 gmc c15 heavy half keeps killing its battery, this started after I replaced all the bulbs in the instrument cluster. Is there any way for me to see if I can find what is killing my battery. Thanks guys!

[jaredts]

I would first use a multimeter to see how many amps are being pulled with everything turned off to see if a parasitic draw is the problem.  You could then start pulling fuses and see when the current draw goes away.

[Ben_Greenberg]

Thanks Jared, should I be seeing 0 amps when off?

[Ben_Greenberg]

Thanks Jared, should I see 0 amps if there is no parasitic draw?

[bake74]

     How long does it take to drain a  fully charged battery ?  What do you have on your truck as extras ?  (anything that is aftermarket that could be drawing power).
     This way we can tell you how to go about checking.  If it is quick, then you might have a direct short.  If it takes days or weeks, then something small might be seeping power.

[Ben_Greenberg]

Takes about 2-3 days of not running to be totally dead.

Everything is bone stock.

Thanks everyone!

[Irish_Alley]

i had a similar problem with my moms e150 but it has a wheel chair lift. i removed the positive cable and put a multimeter and set it on mil amps. with the wheel chair life fuse in it was (dont remember the exact number) .090, with the fuse out its .002. for some reason the lift was using power when it was just sitting there. i rigged up a light switch and ran wires to the back of the van so she could kill power to the ramp when she parked it. sometimes it would kill it overnight other times she would run 5 minutes up to the store and her battery would be dead. once i rigged the switch up it stopped killing the battery.

 so she took it to the guys who put the lift in told them what was going on and what i did.  they looked at it and said what i did doesnt do anything and the lifts not the problem. but they would leave the switch in place if she wanted them to.

[Irish_Alley]

also i think the normal things that drain batterys are stereos/amps, alt and ecu

[bake74]

     Refer to the 1978 Wiring Diagram in the tech section for electrical diagnosis of the 3 possible electrical problems.
     Of the 3 you probably have a grounded circuit or a shorted circuit that is draining your battery.
     As Irish suggested, you are going to have to use a made up/bought test light and volt meter to trace down the problem.  Sorry it is not a easier answer to your problem but electrical can be tricky and there could be hundreds of things that could be the culprit.
     The best thing you can do with electrical problems is attack it with a plan and go systematically through your check list.  So see the link to the 78 manual wiring diagram above and follow it's diagnosis procedures.
     Good luck and let us know what you find.

[VileZambonie]

search "parasitic draw" on here and you will find plenty of answers

[Ben_Greenberg]

Alrighty. So I got the battery all charged up and used my voltmeter to test the amperage running through by bridging the batteries positive terminal and the cable meant for the positive terminal.

And I got nothing.

I did read on another thread that a dieing alternator can kill the battery due to some internal issue and that if the alternator is  warm when the truck is off this could be a sign of an alternator problem.

Thoughts?

[VileZambonie]

So you took your fully charged battery, disconnected the positive cable, installed your meter in series and checked for voltage? You should be measuring current (amps) and then scale down to mA or use a test light if you don't have an amp meter.

[Ben_Greenberg]

2 things
First, I'm an idiot, second I was measuring mA and maybe there is something wrong with my voltmeter, but I wasn't getting any reading of a draw.

Now, back to the first point, I thought the headlight dial was supposed to be turned all the way to the left to be off.... Well I had it like that and of course that was wrong so my floor light had been on this whole time! I have been working on this truck during the day so I never noticed this issue, I happened to walk by the truck last night and saw the light on and turned the light dial all the way to the right to turn that off. Now we will see what happens.

Still pretty odd that I saw no draw when measuring mA although my pocket voltmeter may not measure in small enough units to have noticed that draw.

The confusion continues. I will post back up here if everything is ok. I will also post if I come home to another dead truck.

[VileZambonie]

You probably blew the fuse in your meter