Yet another instrument Question

I recently installed a new speedo cluster, complete with new fuel and temp gauges. Everything works great as long as I have a 1/2 tank of fuel or less.

Last night I filled up the tank and noticed that fuel gauge went to full, as expected, but the temp gauge increase to nearly maximum temperature. I don't believe that it all the sudden was running hot but it seams like its being distorted by the fuel tank reading full.

Any one have any suggestions?

 

I would check that little voltage strap the connects the two, make sure it's clean and making a good connection.