Coolant temp gauge problem

The gauge housing is grounded. The harness has a dedicated ground wire that attaches to the cluster with a screw. The voltage regulator is grounded to the same screw. The regulator is putting out a solid 5 volts. The fuel gauge itself doesn't have a ground at the cluster.

I used a wire wheel and cleaned the block, firewall, frame and also cleaned all of the wiring terminals. I removed the sending unit and cleaned it and the block. I ran a wire from the battery ground to the body of the sender just in case, still nothing.

Ill try to switch the coolant temp wire with the fuel gauge wire and see what happens.