I’m new to the forum so sorry if this is in the wrong place. But I have a 2002 E450 with the 7.3 that had a non working fuel gauge. I pulled the sender, resoldered a bad wire and now I get the proper reading from 16-160 ohms. When I plugged it back into the truck (outside of the tank for testing) the fuel gauge doesn’t move. But if I hold the sending unit in a certain spot, then turn the key on the gauge moves to that spot, but any movement after that and the gauge doesn’t move until the key I recycled at which point it stays in the new spot regardless of where the sensor is positioned. Any input thanks!

 

If the level indicator in the instrument cluster moves when the sender is moved through its range of motion but becomes intermittent I would suspect the sending unit rheostat having a dead spot along its path.

 

You have to ground the tank pump sender assembly if it's out of the tank
You did that right?
I remember the Dealer days of pulling the gauge cluster and ohming out wires back and forth from the tank
Some had bad gauges and some bad wiring