Strange issue troubleshooting a parasitic drain.
Strange issue troubleshooting a parasitic drain.
(OP)
I am chasing down a parasitic drain on a 1995 Mustang that someone put a 97 Cobra motor and trans in. I think they used the wiring harness from the Cobra. They also added wires for the convertible top and rear windows. Anyway, what is strange to me is, I took the Positive cable loose and put a test light between the POS terminal and POS lead and it lit up, indicating a drain, but if I put the test light between the NEG battery post and the POS battery cable, I am showing voltage. How can I have 12V on the POS cable with the battery disconnected? What in a car would have capacitance? If I short the POS cable to ground, of course it goes away, like discharging a capacitor. I don't think it has air bags or an amp with a capacitor but does have ABS and a security system. Any ideas?????





RE: Strange issue troubleshooting a parasitic drain.
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Strange issue troubleshooting a parasitic drain.
And note, almost all cars have some level of continuous loads, to include the clock, any interfaces for key fob remotes, and the battery's own internal parasitic load.
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RE: Strange issue troubleshooting a parasitic drain.
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RE: Strange issue troubleshooting a parasitic drain.
RE: Strange issue troubleshooting a parasitic drain.
RE: Strange issue troubleshooting a parasitic drain.
It's not common, but it has been done, mostly to cars that are valued.
9.5 amps drain with everything off suggests a wiring error or a chafed harness.
That should produce some heat.
So get an infrared thermometer and survey every inch of the harness.
Have someone watch your drain ammeter while you are removing carpet and fiddling with harness. If the drain changes suddenly, you have found at least part of your problem.
Mike Halloran
Pembroke Pines, FL, USA
RE: Strange issue troubleshooting a parasitic drain.
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RE: Strange issue troubleshooting a parasitic drain.
RE: Strange issue troubleshooting a parasitic drain.
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RE: Strange issue troubleshooting a parasitic drain.
There are also some other consumers of power. For example, I have a 2001 Mazda. If you unlock the doors with the Keyfob, the doors will automatically relock if not manually opened in approximately one minute. So there is some control circuit monitoring the door operation.
On a BMW, if the battery is not fully charged, the anti-theft system will not fully engage, which then causes a very high drain on the battery.
RE: Strange issue troubleshooting a parasitic drain.
Some auto parts stores carry current indicators that work on this principle.
Bill
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