fuel pump relay

[Suburban6.0swap]

could be either. Never could get the fuel guage to work, ground and purple signal wire are closed, but still cant get it to show anything but full, so there is some type of problem there - did work after fuel pump was put in the tank, but not for long. also hooked up the power to the junction block (that comes off the starter) to ground at one point and saw some smoke from the wire that goes to the alternator, luckily alternator is still fine and everything else, but this may have been what got it...o well back to work...

[GasGuzzler]

That smoke show more than likely burned a fuse link. There are several at the junction block.

What do you mean by "ground and purple signal wire are closed"? On that style, the pump and gauge ground through the black wire I believe. The purple should go from the gauge to the sender in the tank. When resistance is infinite, the gauge reads full.....so when the purple wire (anywhere from front to rear) is open (or cut, or unplugged, etc.), you'll see full on the gauge.

[Suburban6.0swap]

The fuel gauge signal wire is purple terminal W at the instrument panel plug and goes to the sender. From the sender, there is a ground black wire at the top front of the engine (G110) according to my diagram but I've seen plenty of these trucks that have the ground under 13mm headed bolt at the back on the frame. If either of these circuits are open, the gauge will read full. A short to ground in the purple wire anywhere between the tank and the gauge will make it read empty.

Also make sure pink terminal E at the transmission plug is hot all the time the key is on.

-you are right, the ground is at the back of the frame - its ok. purple wasnt open either.

[Suburban6.0swap]

what is the harm in running without the fuel pump relay?

[RedHeartbeat]

its too simple to screw up. Don't bypass it. The PCM sends out a ground signal to the relay that triggers power to the fuel pump. It shuts the pump off a couple seconds after the engine dies. If you had an accident and couldn't turn the ignition switch off you would be feeding fuel to a possible fire if a hose broke.

[LS1GMCTruck]

What Red said. The computer sends a "ground" signal. NOT a 12 volt positive signal. There is sometimes some fuel pump relay wiring confusion on this subject.