Temp gauge bouncing from cold to hot and back to cold over and over again.

OK I did not realize the fuel ga. was working. That eliminates the RTE. You are down to connections/ problems on the pc board, and the gauge itself. One thing you can do is pull the gauge and power it with a flashlight battery or two. I have forgotten--try to find the thread. Either 1 or 2 1.5V will bring the gauge up some