GM did have a lot of Engine Computer trouble around that time period, and they often acted like they had bad solder connections, but given the age of the truck, that computer has probably been replaced a couple of times already. Also, the computers often caused stalling or no-start conditions, but not blowing fuses. I would be more suspicious of a wiring problem like the wires to an oxygen sensor heater falling down onto hot exhaust parts, melting, and grounding out.
A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.
For intermittent problems like yours the bulb may be dim already. Watch what takes place when it gets bright. That's when the short is occurring. It could be due to the rocking of the engine when you shift between reverse and drive. It could be due to the body flexing when you drive over bumps in the road. The bulb limits current to a safe value when the short occurs, in this case about one amp. If the engine won't start with a brake light in the circuit, try a headlight bulb. The low beam filament will limit current to five amps, and the high beam filament will allow about six amps to flow.
Sunday, February 16th, 2014 AT 4:18 PM