I have an 85 F250 that had dual tanks in it. It was converted to carb and the front tank was pulled out. I recently removed the remaining tank in favor of a 33 gallon bronco tank from an 82 parts bronco. It has the old style 2 prong sending unit harness. I'm trying to find the "hot" wire on the 4 prong connector in my truck to make the sending unit operate properly. I have 5 gallons of gas in the tank and the gauge is reading below empty. Can I splice into the existing harness and make this system work? I havent been able to find a good wiring diagram for the fuel system either so if anyone has one it would be a big help.

 

This diagram says you need the yellow/white for the gauge, and you will also need the black wire to ground the sending unit.