Fuel gauge not working on a 79 CJ7

I currently own a 1950 cj3a and a 1979 cj 7 . The fuel and temp have never worked and both have been replaced with no improvement. My question is the temp gauge uses 5 volts does the fuel use 5 volt or 12 volt. I have 1 amp 5 volt regulators that could be used to power the temp gauge and if the fuel gauge requires 5 volts a second regulator could be used. I would like the temp to work the fuel at this point is optional. (I can still walk or write down the mileage)

 

I feel like all fuel gushed can run on 12v. I’ve done other gas tanks and there’s a way to ground out the sensor to see if it’s getting voltage. Then diagnose the sender or the gauge.

 

Typically with fuel sending units, the sending unit is the ground and the change in the resistance dictate full or empty.
if you take the wire off of the sending unit the gauge needle will bury past full and ground it to a good ground and it will go to empty, if my memory serves me correctly. So if your gauge is getting power and not faulty, this method will isolate the problem and tell you if its a faultily sending unit or not. Hope this helps
You can also use ohm meter and test the sending unit and see if the resistance changes an you move the arm of the sending unit up and down.