electrical short?

[caminofan]

Hello all. I need to pick someone's brain. My battery keeps draining on my 04 trailblazer ext. I bought the battery over the winter,but I tested it anyway. Load tester shows the battery is good and that the charging system is functioning properly. My guess is there is a short somewhere in the electrical system. Battery draws down and won't crank after only a few hours, but runs fine after getting it started. Anybody have any ideas where to start searching for short? Thanks

[Tony Silva]

Pull the negative cable from the battery and clip a test light to the body structure of the car to the negative post on the battery. If there is a parasitic draw then the test light will light up. With the test light on...pull and reinstall each of the fuses one at a time untill the test light goes out.

But this trick ONLY works if you have only one bad circuit. If you have 2 bad circuits then the test light wont go out because obviously you aren't going to be able to know which 2 fuses to pull out at the same time to make the light go out.

If the test light does not go out, don't just automatically assume that you have 2 bad circuits. Make sure that you pull the fuses in the engine compartment too, and just not the ones in the dashboard. Also pull the fusible links too while performing the test light trick.

Also, NOT every circuit on the truck has a fuse or a fusible link protecting it. Some circuits have a curcuit breaker. I would next...one at a time...remove and reinstall each electrical socket I could find on the entire truck....checking the test light every time. If I can't find the problem, I would then take it to an electrical shop for diagnosis (only) and do the repairs my self.

[Schurkey]

Originally Posted by caminofan

Load tester shows the battery is good and that the charging system is functioning properly. My guess is there is a short somewhere in the electrical system. Battery draws down and won't crank after only a few hours

A FULLY CHARGED battery that drains down after "a few hours" has a MASSIVE drain that will be easy to find.

[caminofan]

Thanks for the advice Tony. I did what you said and did manage to find a smaller draw on the system. Test light got dimmer when I pulled fuse for onstar, but there is still a major short somewhere. I went as far as removing the entire onstar control module, but that wasn't a problem. A friend used to be a tech at a chevy dealership, says that chevy is notorious for putting modules in places where they are exposed to weather and such. Guess I'll have to bring it to dealer to be put on computer.

[Schurkey]

Have you actually measured the amperage of the draw?

Have you cleaned the battery case?

[maxwedge]

It is tough to look for a draw this way as some modules stay alive for 5 or 10 minutes then shut down, every time the battery is disconnected and reattached the modules start up again, you need a external amp gage such as electricians use to check the draw 10 minutes after shutdown.