Join Date: May 2017
Location: Bossier City, Louisiana
Re: Odd Battery Issue
My bet is a faulty alternator that has a bad diode in the rectifier that is mentioned above. The diode fails towards ground which allows alternating current to pass through to your electrical system and drain your battery while sitting.
Use your multimeter to test for AC at the battery while the engine is running. But make sure you know how to interpret the autoranging screen on the meter because reading small amounts of AC can be tricky. A good alternator should pass no more than .02 volts AC.
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1970 El Camino under Reconstruction - 5.3L LS VORTEC Engine and 4L60E Transmission