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Silly Electrical Question, but need an answer anyway.

Hi all,

'91 lumber wagon (1/2 ton), 305cid, 5 speed, 10 million miles, almost ready for the boneyard, except it runs great! Seems I have an electrical short somewhere. I run it, shut if off, the next morning the battery is dead. Jump it, run it, next morning it's dead. Pulled the battery out of my '95 and the problem is duplicated. New alternator and ECM this past summer.

I know there's a trick where you disconnect one of the battery cables, put a test lamp between the cable and the post, and start pulling fuses. When the lamp goes out, you start checking the curcuit from the last fuse pulled.

Question is, which side do you do this on, positive or negative. Before I rip into it, I want to make sure.

I'm pretty sure it's the lighting harness in the back, as it appears a band of drunks wired different trailer harnesses up over the years.

And lastly, Thanks, Merry Christmas to all in the group!

Rick K

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Reply to
nobodyhere
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first off:

just because the alternator was 'new last summer' doesn't mean it's good now

the first thing I'd do is disconnect the big red wire from the alternator and leave it overnight with battery hooked up

if battery is OK the next morning you've found it

if not, then I can talk you thru the procedure you were asking about

G

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Reply to
Gary Glaenzer

Doesnt matter which cable, but messing with the neg is safer. After you hook it up you can pull the fuses and the alt wire like Gary said and try to find it. GL

Reply to
Scott M

First you want to make sure its not the alternator causing the problem. I don't know if you have both positive and negative posts on the alternator, and that if you have the negative that its not also shorted thru the case. So I'd start by removing the negative from the battery. Then the positive from the alternator. Then reconnect the battery.

If the bulb lights thru the alternator then you have found a problem. It may not be your only problem.

If its not the alternator then I'd simply pull fuses and momentarily replace the fuse with the light bulb. When the bulb lights that circuit is drawing power. Make sure the dome light isn't on.

I'd use the bulb fist on the fuse circuits to test for large current draws. If the bulb doesn't light I'd follow with an ammeter. IIRC there should be less than 1 mA draw with the vehicle off. Actually, there should be 0 mA draw but you might have a clock, and the ECU might draw one mA maintaining its memory.

It takes more than 1 amp (1000 mA) to draw a battery down overnight.

Reply to
David Kelly

Thanks - I never thought about disconnecting the wire from the alternator. Figured since it charges up real good after I jump it, it's ok. Must have been some mental block or something. I'll give that a try first, then start messing with it.

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Reply to
nobodyhere

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