Dear Tom and Ray:

Our 1990 Chevy Lumina mini-van has an electrical problem. The interior lights have a main switch up front on the ceiling--between the front seats. The switch was replaced. Since then, the fuse continually shorts out, causing the interior lights and the power door locks to shut down. No other circuits are affected. The dealer insists the switch is OK, yet they cannot find any other problems. What do you think?
Dave

RAY: I think you must be too nice a guy, Dave. And I think you've been too nice too long in this case. Obviously, you've got a short somewhere in this circuit. And your dealer, due to either lack of interest, lack of profit potential, or plain old stupidity, hasn't made a serious attempt to find it.

TOM: First of all, rather than insisting that the switch is OK (which it probably is), they might as well TRY replacing it again. That's the simplest thing to do, and it only costs about 80 cents. At least you could rule that out before going on to more complicated diagnostics.

RAY: The next thing I'd do is disconnect the power windows from the circuit. That will tell you whether the problem is with the windows or the lights. If you unplug the window wiring harness, and your circuit is still shorting out, you know your problem is in the interior light wiring.

TOM: And the way you find a short is by figuring out where it's NOT. You continually narrow down the possibilities until you isolate the location. Then, once you've found it, you replace the bad wire, bad switch, or bad fixture, and go on with your life.

RAY: Tell them to start by giving you a new interior light switch, Dave. And tell them if that doesn't fix it, you're willing to pay them to do the work. Once they have that crucial piece of information, I'm sure they'll be more than happy to remove your shorts.