[gaseousfool]

Hi all. I am sure some of you know this but just in case... The power to the electric fuel pump runs through the oil pressure sender (grey wire) once the vehicle has started and the key is in the run position. The reason for this is safety. If you are in a accident and the fuel line is severed due to collision damage the fuel pump will shut off once the engine quits. GM doesn't want the fuel pump to spew gasoline all over the place in case of an accident and the unfortunate guy or gal forgets, or is unable due to injuries or being trapped inside the vehicle, to turn off the key (whether the engine is still running or not). During initial key on and cranking there is a starter bypass that feeds current to the fuel pump and bypasses the oil pressure sender. This will also (hopefuly) prevent engine destruction if you lose oil pressure while driving and don't realise it. The engine will die, due to fuel pump shutting off, and not cause further damage to itself.
Also for those of you listening for the fuel pump at the gas filler, when you turn the key to run, the pump will only go a few seconds and then stop unless the engine computer see's an RPM signal from the engine (engine needs to start to see this signal). This is another safety feature. When listening for the pump you may need to cycle the key several times.
Also someone said to jump 12 volts to the short single wire that breaks out of the wiring harness just below the fuel pump relay. This is the proper way to test the pump, thats why that little wire is there in the first place. Good Luck!