What I do is use a continuity test light. take off the POS. battery cable and connect the light between the cable and the battery post. If there is something grounding the light will come on. Next go to the fuse box and pull one fuse at a time until the light goes out. This will get you to the circuit the problem is in and now all you have to do is get a schematic or trace wires until you find the source. But do not overlook the diode in the regulator of your alternator.
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