Sorry in advance for long post. I am installing repo rally pac. Bought new many years ago at Nationals. Reconfigured wires in dash. Checked many times, correct order. Fuel gauge goes past full. I have cleaned all connections from trunk to main harness by fuse box up to fuel gauge. With the sending unit unhooked, checking tan wire in trunk at main harness, I get around 66.5 ohms. If I ground this same tan wire, fuel gauge goes to empty. When I unground it and turn on ign, it buries full again. Now if I pull gauge cluster and unhook harness and recheck resistance in trunk at tan wire I have .2-.3 ohms. The sending unit is unhooked this whole time. I did ohm sending unit while adding gas to tank and the resistance did rise as fuel was put in which tells me sending unit is working. What am I missing?

 

I moved your thread to the Electrical forum. The problem is not in the wiring or the gauge install, it's that there is no ground through the sending unit in the tank. You proved this by grounding the tan wire and driving the gas gauge to E and while ungrounding it goes past F.

 

so would the fix be to drop tank/remove sending unit and clean mating surfaces? Tank was repainted and sending unit replaced years ago, with very little use to date. I did ohm ground wire at about 1 ohm and it is going to good ground when hooked up.

 

Check the tank and sending unit grounding. Run temporary grounds if you have to, the sender is the negative side of the gauge.