I just got a 1966 corvette and the temp gauge works sometimes and then it will get pinned way past the hot mark?What is this a bad gauge or not grounded?

 

It sounds like it's grounding out. You may have a bare spot on the wire somewhere.

 

Welcome to the forums. Check the wire going to the temp sender, look for wire frying or there could be a possibly the Temp sender could be going bad. Try removing the temp wire with the key on and see if the gauge changes.

 

Welcome to the forum.