Replace the blown fuse with a pair of spade terminals, then use a pair of small jumper wires to connect them to a 12 volt light bulb. A brake light bulb should work fine. The circuit will not work normally because the bulb will limit current to a value that's too low, but it will allow you to search for the short.
When the short is present and the circuit is powered up, the bulb will be full brightness, so don't allow it to contact the carpet or plastic door panels. When the short goes away, the bulb will dim. Since it's trying to pass enough current to run the high-current AC compressor, the bulb might be real bright when the short is gone too. That kind of defeats its purpose of being an indicator. If that happens, replace the low-current brake light bulb with a higher-current head light bulb. That will be much dimmer when the short is gone.
Now you can do things to see what makes the short appear. If it does when you shift into "drive", look for a wiring harness that is being tugged on when the engine rocks. If it also occurs when shifting into drive without the engine running, look for a wiring harness that's rubbing against the shift lever on the transmission. If you can get the bulb to stay bright, without the engine running would be even better, you can run under the hood and start disconnecting things one at a time, or moving wiring harnesses around to see what makes the short go away. That will help you narrow down the cause.
Thursday, September 1st, 2011 AT 6:23 PM