Electrical issues...

[Mike's '84]

Why does my battery run down after one day of sitting in my Blazer? What can drain the battery this fast? Just got a new battery and went out the next day and it was dead. The alternator is obviously not putting a charge while its running, because it shows neg. charge at an idle. Put a load on it and rev it up, it goes further neg. I understand that. Going to get an alternator today. But what would drain it overnight in my driveway with nothing on?

I was thinking a window motor or something like that shorting out?

For now I am taking the battery out at night.

 

[73k5blazer]

It sounds like your '84s volt gauge is wired backwards, to the positive wire to the neg terminal on the gauge. Your alternator is probably fine. If you wire a volt gauge backwards, it works but just reads opposite, like if I take my meter and hook the red probe to the neg terminal on the battery and the black probe to the pos terminal on the battery, it will read -13.5v. As you rev your engine, if it goes further neg, then it really sounds to me as if the gauge is just wired wrong. Easily diagnosed if you have a meter you can hook the the fuse box somewhere to see your real voltage.

Concerning your short, well, these are problematic to diagnose. They are tough. If there's something you've played with recently concerning the wiring, you might start with that. Barring that, If you have an good ammeter, you can go one circuit at a time and see which one is pulling load where it shouldn't be, most regular meters will do up to 10amps which just might be good enough to find your problem. Barring that, start the diagnosis by disconneting one fuse at a time before I go to bed. If battery dead, put that fuse back, and pull another the next night. You might want to use a junk battery, or get your battery warrantied after you've fixed it because draining it completely for days on end is inherently bad for it, most normal car batteries won't hold much of a charge after you drain them several times.

 

[Mike's '84]

It sounds like your '84s volt gauge is wired backwards, to the positive wire to the neg terminal on the gauge. Your alternator is probably fine. If you wire a volt gauge backwards, it works but just reads opposite, like if I take my meter and hook the red probe to the neg terminal on the battery and the black probe to the pos terminal on the battery, it will read -13.5v. As you rev your engine, if it goes further neg, then it really sounds to me as if the gauge is just wired wrong. Easily diagnosed if you have a meter you can hook the the fuse box somewhere to see your real voltage.

Concerning your short, well, these are problematic to diagnose. They are tough. If there's something you've played with recently concerning the wiring, you might start with that. Barring that, If you have an good ammeter, you can go one circuit at a time and see which one is pulling load where it shouldn't be, most regular meters will do up to 10amps which just might be good enough to find your problem. Barring that, start the diagnosis by disconneting one fuse at a time before I go to bed. If battery dead, put that fuse back, and pull another the next night. You might want to use a junk battery, or get your battery warrantied after you've fixed it because draining it completely for days on end is inherently bad for it, most normal car batteries won't hold much of a charge after you drain them several times.

Haven't played with it lately. The smog guy did though come to think on it...passed in December 2007.

And I didn't even change the oil.

Anyway I get to play with it today...Thanks for the ideas.

 

[BKinzey]

Could be a bad battery. I'd have both the alternator & battery checked and then do the fuse tests. Check your battery connections, etc.

There are a lot of variables and it could be more than one thing so you need to start eliminating them one at a time.

 

[Thunder]

Sounds like a bad alternator to me. If the diodes blow and short it will drain the battery fairly quick.
Also will show - charge when engine is running.

 

[broke73]

Finding a short

To find the short causing your battery to drain.
1. Disconnect the positive and Negative leads from your battery.
2. Get a multimeter (if you don't have one they sell them at Harbour Freight for about $10.00) set it to OHMS connect one lead to the positive and one lead to the negative.
3. You should read open or a pretty high number open will say OL, shorted will be 0 or right around 0.
4.Start pulling fuses until the meter reads a high number or open. If you pull all the fuses and it still reads a short start looking under the hood at the starter wires alternator etc.