My fuel gauge stoped working so I pulled the fuel tank and the steel arm had come off. I have the arm back on
now and reading variable resistance on my ohm meter
but the fuel gauge is still stuck on empty. There is no voltage coming from the plug.

Thanks

 

Correction, there is 5v between the 2nd and 4th terminal of the plug and if I disconnect the battery terminals and plug in the sender unit the fuel gauge will start to rise and then go back to empty until I disconnect the battery terminals again.

 

The wire arm came off the variable resistor on the sender unit so I epoxied it back on so it can't come off again. I also found a severed wire on the drivers side under the door hinge area. Fixed wiring and fuel gauges works now.
Thanks to Dinner and espanton at Fuel gauge problem - not sender - Dodge Diesel - Diesel Truck Resource Forums