Help With Fuel Gauge Not Working

[Rickmustang]

I'm working on my neighbor's factory pink/white interior 289 4-speed convertible. The gas gauge is not working, or only works inaccurately. My guess was a hole in the float. I pulled a C8 FoMoCo fuel sending unit out of the tank and the float was good. Does it matter that it is a C8 unit? I then grounded the fuel sending unit wire with the key on...the gauge did not move. How do I test the fuel sending unit? Should I test the output of the instrument panel voltage regulator? Next steps?....I'm a little stumped. Thanks.

[Bob Gaines]

I'm working on my neighbor's factory pink/white interior 289 4-speed convertible. The gas gauge is not working, or only works inaccurately. My guess was a hole in the float. I pulled a C8 FoMoCo fuel sending unit out of the tank and the float was good. Does it matter that it is a C8 unit? I then grounded the fuel sending unit wire with the key on...the gauge did not move. How do I test the fuel sending unit? Should I test the output of the instrument panel voltage regulator? Next steps?....I'm a little stumped. Thanks.

C8 unit will work  fine. The only difference is the 3/8 outlet vs. the factory 66 5/16 outlet . If you ground the sender wire to the gauge then the gauge should go full tilt. If not then there is at least a problem from the wire to the gauge side of the system . Wiring ,constant voltage regulator or gauge are all suspects until ruled out otherwise.

[Rickmustang]

Thanks Bob. Would the instrument voltage regulator affect the function of the other gauges?..they seem to be ok.

[Bob Gaines]

Thanks Bob. Would the instrument voltage regulator affect the function of the other gauges?..they seem to be ok.

Typically the constant voltage regulator for the instruments would logically effect all the gauges if bad but with that said I recently heard of a instance where that cleared up a fuel gauge problem where all other gauges were working perfectly so the OP said. The caveat seems to be that the aftermarket instrument constant voltage regulators are unreliable so I have heard several times from others recently. NOS or confirmed good used seem to be the best choices.

[s2ms]

This is the thread Bob is referring to...

https://www.saacforum.com/index.php?topic=22273.0