All you have to do is whatever it normally takes to cause the fuse to blow. If that happens without running the engine, you won't have to run the engine.
If the short is gone when you unplug the neutral safety switch, all you know is it is somewhere between that point and the backup lights. I never autopsied a switch to see if it shorting is possible, but regardless, a pinched, bared, or rubbed-through wire is more likely to be the cause. You can forget about the other things in that circuit because if one of them was shorted, the fuse would blow all the time, not just when shifting into reverse.
The closest book I can find is for a '92 Buick Park Ave, and the transmission range switch is different, but if they use standardized wire colors on all models and years as most manufacturers do, the pink / black wire brings 12 volts down to the switch, and the light green wire sends that current to the backup lights. There could be a light-monitoring module in that part of the circuit too. The wire colors could easily be different on the switch, but if you have those color wires in the electrical connectors to that switch, you can unplug those connectors, then use a jumper wire or stretched-out paper clip to connect them. That will totally remove the range switch from the circuit. If the test light is still bright, you'll at least know the switch is not at fault. If the test light is dim and the backup lights come on very dimly, you'll know the circuit is working. At that point you can replace the test bulb with a fuse and the backup lights will be full brightness.
Tuesday, January 10th, 2012 AT 3:31 AM