The car is a 1968 442 HT. I replaced the gas tank, sending unit, soldered the ground with to the unit, I've tried several grounds, I even repaced the sending unit wire in the trunk. The gauge is stuck on "HOT" and does not move.

 

You need to disconnect the sending unit wire at the back of the gauge and then ground the gauge terminal that you removed the wire from. If it does not go to E and you have 12v on the other gauge terminal your gauge is faulty. If it does go to E then your problem is an open wire from the gauge to the trunk.