fuel pump wires

whiplash · December 2, 2006

Thanks for your help with the relay. I have another fuel related issue. I need to find the positive and negative wires for the fuel pump, at the fuel pump. From what I can see with a mirror there are two connectors at the forward top side of the tank, and I am assuming that the larger connector is for the pump. I need these wires for my MSD boost-a-pump, and I took my meter and checked the wires for the larger connector at the inboard side of the top of the tank near the driveshaft. I found that the larger of the two black wires, and the gray wire would give me negative and positive, respectively. With the key switched to on, I would see 11.5 volts for about 5-7 seconds, then back to zero. However, when I spliced in the booster, I no longer had power for the fuel pump. I have already installed a STS Turbo system on the truck, and I only have the MSD and an alcohol kit and tuning left to go. The MSD senses boost from the manifold and then raises output voltage to pump in relation to boost increase. I have noticed that the purple wire will also give me switched voltage at the pump as well, and I have hit a wall with trying to straighten this out. I need the wires as close to the pump as possible because the factory wires are not large enough to handle the increase from the MSD booster over a long run. If I hook the wires back up normal at the tank, the truck idles fine. I am waiting on a factory service manual, and again it is an '05 GMC Sierra 1500HD 6.0L with Quadrasteer. Any help you could give me would be extremely appreciated!!!! Thanks again!