Fuel gauge malfunction
 

I am still trying to track down the reason for my fuel gauge periodically acting like it's grounding out and pegging itself past the full mark. I'm driving along and it reads properly for awhile and then will peg to the right for a while. I have traced the wiring from the fuse block to the cab hole and as much of it under the frame as I can see while laying under the truck. This is a replacement gauge that gets its signal from an LMC tank mounted in the frame. Is it possible that the problem is the gauge itself? I has worked fine for the 5 years the replacement gauge has been installed. I recently had some stereo work done and they ran the speaker wire along with the fuel gauge wire down the drivers side floor trough. As it seemed to start acting up after the stereo work I suspected something wrong with the wire in the cab but it seems OK. My next step is to get the truck up on a hoist and examine the entire length of the wire from the cab back to the tank. From what I can see the connection to the tank terminal seems solid. When wiggled with a screwdriver it does not affect the guage. The tank is up tight to the frame and I can see the connections but can't quite get my hand in that far. Any help appreciated.

Re: Fuel gauge malfunction
 

Your symptoms are characteristic of losing the connection from the tank sender unit, not from grounding out. A lot of the problems have been found under the drivers side sill plate over the rocker panel.Your inspection seems to rule that out. You may have lost the ground from the tank to the frame or from the sender to the tank.
Try grounding the tank sender wire and see if the gauge returns to empty. If it does then the wire is most likely good and the problem is the tank or sender.