There are a number of times when you might want to run your lift pump without running the truck. For example, you will need to purge the air each time you change a fuel filter. Or, if you ever run out of fuel (or just run low enough on the trail for the pickup tube in the tank to suck air when you get onto an angle) you will also need to purge the air out before the engine will restart. Diesels love to run and run once they get started, but a little air in the system can make getting it going in the first place a real pain.

Another case where jumping the lift pump might come in handy is if your oil pressure sender fails (in an NA diesel Hummer, your lift pump will not run without a positive signal from that sender!)

Whatever the reason, it is good to know how to "jump the pump." You could buy a pre-made switched jumper setup like the ones that BlueHummer Outfitters sell, consisting of a couple of alligator clips and a connector. Simply disconnect the 2-lead connector that comes off the lift pump, and plug in the jumper setup. Connect the red alligator clip to a 12v positive power source, and the black one to a ground. Click the switch and that lift pump should start whirring.

Steve Brajak, a Hummer H1 mechanic at my local dealership, showed me a shortcut for jumping the pump, and it is the method I use regularly. First make your own little jumper wire. In only needs to be about 2 inches long, and a simple spade connector crimped onto each end will do the trick. If you like, clip one of the spade connectors with diagonal snips to make it narrower; this will make it easier to insert.

Next, locate the relay for the lift pump. Facing the truck from the front, it is located in front of the fuel filter, to the right of the cable lock for the hood latch. Unclip the relay and pull it down, and you will expose the connections as pictured. Place one end of the jumper wire in the middle connection at the bottom. Place the other end in the connector that is diagonally above, as pictured. This will run the pump without any other extraneous wires in the engine compartment... quick, simple, and neat. And it saves wear and tear on your starter motor to purge the air this way instead of cranking the ignition over and over.