I recently acquired a 1986 Crown Vic with 86000 miles. The fuel gauge does not operate properly and I desperately need help moving forward. When I jump the wires in the connection at the tank the gauge immediately goes to full. When I remove the sending unit, connect an OHM meter, I get readings that indicate it is working properly. When I reinstall the sending unit and connect the gauge wires, I get an empty tank reading. Can anyone give me an idea on where to go next, what could be causing this. When I read the volts at the terminal wire I get about 7.5 volts. I am at my wits end and at the limits of my knowledge and will greatly appreciate any advice on what to do next.

 

Key on, fuel pump removed, fuel pump level wires connected, slowly swing the fuel pump level arm through its arc and watch what happens with the fuel level indicator then.

 

The fuel pump and sending unit are located at different locations, the electric fuel pump is on top of the tank, which requires removal of the gas tank to remove. The sending unit is located on the front side of the tank, which can be accessed with the tank in place. Are you telling me the pump and the fuel float can be interfering with each other? This is my first Crown Vic.

 

In that case just remove the fuel level sensor.
Yours is way way older then what we see at the dealer so I was unaware they had different fuel pump/level sensors. Now a days its all one part.

 

I'll do that next, I'll have to burn some fuel first so I can remove the unit. By any chance do you know what kind of voltage I should have at the sending unit?

 

No idea sorry, online workshop manuals stop at 1992 if memory serves

 

Can anyone tell me what voltage I should have at the connection to the fuel sending unit?

 

Finally gave up and ordered a new sending unit, every things working fine. It blows my mind that the two units work good separately but will not function together.
Thanks to everyone that gave me advice.