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.
Remove the positive and negative cables from your battery and connect them to an ohm meter, preferrably a digital type, for they are easier to read. Normally, the amount of resistence between the cables would be very high- a reading above 10k ohms would not surprise me. (You may want to measure this on another car to give you an idea- which does not have this problem, of course!) However, if there was a short somewhere which caused your battery to be drained overnight, I would expect to see a much lower reading, perhaps below 500 ohms. Even the memory in your radio requires a negligible amount of current to operate.
To isolate the source of the short, I would start by removing fuses, beginning from the BATT source. Watch the ohm meter each time to determine if the resistence increases substatially. (And no light bulbs are on when they shouldn't be, right?) If you do not see any difference, try unplugging other possible sources of direct shorts: key switch, neutral safety switch, headlight switch, power to the starter, etc.
It may be as simple as this, however in my experience it doesn't always turn out that way! Let us know what happens.
Go out after dark and check for underhood light, brake lights, glove box light. If it has a trunk light, make sure it goes out before the lid is down. Pretty common for something like this to stay on and drain battery.
Use the test light method above, go around and pull fuses until it goes out. Don't forget the dome light is on when the door is open.
If there isn't enough drain to light a test light, then use the ohm meter method.
I like the light because you can position it so you can view it easily when working on the car circuts.
I'd disconnect the hot lead on the alternator and test it too. A shorted diode inside the alternator will drain to ground thru the hot lead.
Check my web page for suspension info: David's Homepage
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