i have a 90 f150 when i switch it on the fuel gauge on the front tank goes past full n sits there until i turn my truck off please help . could it be a ground if so where do i need to look for the fuel gauge ground

 

Sounds like the sending unit or the wiring going to it is shorted to ground. Unplug the wires at the pump to see if the gauge falls if it does the problem is with the sender if not it's in the wiring.