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Re: Diagnosing short circuit Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 29 Jul 2009 11:51:31 In Reply to: Diagnosing short circuit, abusot, Wed, 29 Jul 2009 07:36:30 Members do not see ads below this line. - Help Keep This Site Online - Signup |
First, I have rarely ever seen a short draining the battery. If the battery has been discharged a few times, it loses the ability to hold a charge. Yes, you can charge it up, but it loses it quickly.
The only exception is a stuck on trunk light.
OK, say that there really is a discharge to trace. Start with a voltmeter that can read current, and a piece of wire.
Roll the windows down, open the fuse box, close the doors, leave the car off.
Disconnect the ground lead from the battery. Jumper the ground clamp to the negative post with the wire. Wait 30 seconds or so. Put the meter, set to amps, with one lead on the ground clamp, one lead on the negative post, and then remove the jumper wire.
After about a minute or so, the normal current drain of the system is about 35 milliamps (0.035 amps). 50 ma is fine. An amp or two, a problem. If you see a large current draw, start pulling fuses one at a time - reach in through the window; if you open the door, you trigger the dome light. If you pull out a fuse and the big current load goes away, you've found the issue. If you don't see a change when you pull a fuse, don't be surprised if the current jumps up for a few seconds to a minute when you plug the fuse back in - many circuits will pull current for a short while when the power comes back on.
Why so much work with the jumper? When you disconnect the battery and then reconnect it, many circuts pull current for a while (as an example, the dome light). If you just connected up the meter, you might pull a few amps, and the fuse in the meter might blow. By using the jumper, it takes the current, not the meter.
However, if your trunk light isn't stuck on (just remove the cover, close the hatch, see that the light goes off, I'll place good money on a bad battery.
posted by 192.249.47...
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