How do I troubleshoot a short in my 2004 Impala LS 3.8l?
The heat killed my car today. I parked it this morning and in the afternoon it wouldn't start. I thought the battery had drained and decided to try cleaning the battery terminals to see if I could coax it to start. As I reconnected the negative, it started sparking! I verified with my multimeter that, indeed, there was 12.8VDC coming from the frame! My guess is that some insulation melted on a wire and shorted it to the frame SOMEWHERE in the car. But isolating it is gonna be a pain. I tried pulling every fuse and relay in all four fuse boxes while my daughter watched for the multimeter to see if the voltage went away but no such luck. (I was hoping to isolate the circuit where the short was.) I left the negative terminal disconnected to avoid any further damage.
Any suggestions on how I might isolate the circuit where the problem is and avoid ohming out every wire in the flipping harness? A new car is out of the question for at least several months and I am a service rep for office machines so I live in my car. (I mean that metaphorically - the pay's not THAT bad - lol!)
Thanks in advance!
MIchael: I appreciate the response. The technique I used was putting the black lead of the multimeter on the negative battery terminal and the red lead on the ground cable (while the cable was disconnected.) It kept a constant 12.8VDC (which was the voltage across the battery terminals as well) for at least fifteen minutes or so. I would have expected, if I were shorting a capacitor, to see the voltage drain (which I think is what you're saying about the lamp dimming) but it just stayed there.
Humvee: I agree that a short isn't likely to just appear while it is sitting there. That's why I thought maybe some insulation melted. The heat was above 100 degrees here today, and this car has 270K on it so if something was marginal, it might have gone. I really didn't expect 12V from ground to ground, but given your answer, maybe I'll take the battery over to Autozone tomorrow and make sure it is fully charged, then put it in and try to start up. This is how the car has acted to a dead battery a couple of times in the past, so maybe it is a "ghost." At any rate, it sure is a gremlin! Thanks for the response.