something draining battery - Ford Mustang Forums : Mustang Forum
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post #1 of 4 Old 01-31-2012, 11:53 PM Thread Starter
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something draining battery

i have a 97 cobra and i just put a new battery in a few weeks ago. i didn't drive the car for a few days and the battery was stone cold dead. what could be draining it? i'm lost.

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post #2 of 4 Old 02-01-2012, 03:44 PM
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disconnect the pos bat cable, attatch a test light in between cable and terminal(it will light up if a draw which im assuming you have. go to the fuse panel and start pulling fuses until the light goes out. Now you know at least what circut is causing it and makes troubleshooting a lot narrower.

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post #3 of 4 Old 02-03-2012, 07:57 AM
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The post above me is pretty much correct. I just don't care for test lights as much.

For me I use a multimeter that has mA setting. First you want to remove negative battery cable. The put the multimeter b/t negative cable and neg terminal on battery. The setting the multimeter should be on first is 10A, unless your multimeter has a lower setting. If you start off with the multimeter in mA you will pop the internal fuse of the multimeter(MM).

Once of 10a setting see what your reading is once setup. This is with key off also BTW. If it shows like 1 or .5 or something like that. Then something is draining it quite a bit.

As said above have somebody start pulling fuses (take note as to where they go) until you all of a sudden see the amps drop. Now change the multimeter to 200 mA or the highest setting for mA. Check and see what it is, it should be lower than 100mA on most cars. Depending on options and accessories your car came with. A manual should tell you what the key off draw should be.

Anyways once you found the problem, look up the circuit wiring diagram and see what all it powers. Usually it's a radio or door switch that give the most issues.

Hope this helps out.
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post #4 of 4 Old 03-01-2012, 12:24 AM
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i had the same problem.. it was the mach AMPs in the trunk staying powered up.... i've also heard if the ignition switch wears it can stay energized when the key is out.... open the door and remove the key... if the door dinger still sounds its the ignition switch... if not unplug the mach amps in the trunk and try that... what i have heard is as they age the circuit that turns them off goes wacky and they still draw power with the ignition off!

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