[James]

I recommend the fuel probe be installed in the gas tank before any troubleshooting can take place for safety reasons.

There could be issue with the power or ground side of the fuel probe. If you have a voltmeter you can test it for a faulty power or ground. But first before doing that let try this quick and easy test. Disconnect the wire from the stud. Connect a jumper to a good ground in the cab. The other end of the jumper to the wire (that goes on the fuel probe stud). Turn the key on. This should make the gauge reads empty.

The following tests must be done with the key on just like you need to read the gas gauge and all wiring connected. When checking be sure to check both side of a connector (i.e. The wire on the fuel probe stud, you would check the terminal then check the stud for power. It should be the same but it could have a thin film of oxidation creating a bad connection.) Also look at the wire where it attached to the terminal, if there any broken strands or a green coloration (corrosion) replace the terminal, this is added resistance.

After the quick test, if it doesn't read empty there is resistance/corrosion between the gauge and the sending unit. Using a voltmeter measure the voltage (check your wiring diagram first) on the back of the gauge. This voltage should be the same all the way to the fuel probe stud.

After the quick test, if it does reads empty use a voltmeter and see if there a voltage drop between the fuel probe base and a good ground, voltmeter should read 0 volts . If you have any voltage move the probe toward the ground point until you read 0 volts.

If you have a change in voltage drop the you have a bad connection (resistance/corrosion). Disassemble, clean, reassemble, and retest.

If you need addition help let me know.