I've checked all of the posts, but I can't seem to find one that fits the problem I'm having, so here goes. This is a '72 GMC pickup. When the tank is full, the gauge reads 1/4-tank. It drops as the fuel level goes down, so it functions that far at least. I replaced the fuel sending unit. Same issue with the new one. Only goes to 1/4 tank when the tank is full. If I disconnect the wire to the sending unit, the gauge goes to full. Reconnected the gauge goes back to 1/4 tank on a full tank. I added a ground strap from the fuel tank to the frame. Didn't change anything. I pulled the ground from the battery and cleaned that terminal connection. No change. I tried raising the arm on the sending unit with the wire connected and the unit grounded. If I raise it all the way up, the gauge goes to about 1/2 tank and that's all. I'm guessing at this point that it has to be the gauge. Since this is a '72, I'm not sure how the gauge is wired. It may be a circuit board (I can't see the back side of the gauges from under the dash). Any suggestions anyone? Any help would be appreciated. Thanks.
