Q: I have a short that drains the battery overnight.

asked by on February 18, 2017

I have tested from negative battery terminal to negative cable using a 12V test light, but the light doesn't go out when I pull the fuses. Also, I get a lot of static in the radio when I rev the engine. Wondered if it might be a diode in the alternator??

My car has 135000 miles.
My car has an automatic transmission.

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There is a parasitic load applied to your battery with the ignition is off. Keep the test light on the battery and turn on one thing at a time and watch the light. If the light goes out, then that issue is the problem. Be sure to have your doors shut and open them to verify the door light switches. If nothing is turning off the light, then remove the power supply harness to the alternator and see if the light goes out. If it does, then the windings inside the alternator are bad and pulling the battery down. If you need further assistance with a parasitic load, then seek out a professional, such as one from Your Mechanic, to help you.

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