Greetings;

If you can make the gauge sweep full scale bu grounding the gauge wire back at the sender, then obviously the gauge, instrument panel PC board, and wiring from the tank to the gauge are all functional; leaving the problem area back at the tank.

All the fuel gauge sender is is a variable resistor connected in series between the fuel gauge wire and ground. As resistance changes, it changes the gauge position. The fuel gauge circuit is designed to operate within a very narrow resistance range, so anything that creates excessive resistance in the circuit can affect gauge operation. You will need a DVOM to test the circuit to isolate the fault.

Possible faults include:

(1) Faulty fuel gauge sender. I am aware you have replaced the fuel sender already, but faulty components are always a possibility. Use the DVOM to make sure that you have continuity through the sender to ground, and that the sender does not drop out (go open circuit) at any point through it's sweep. In our shop, we have taken to always installing OE fuel modules and senders; faulty chinese manufactured components from discount parts stores such as Autozone seem to have a very high failure rate.

(2) If the sender is OK, make sure the electrical plug/ electrical connections to the sender are OK. With the sender removed from the tank, plug the harness on to it and take a resistance measurement through the connections, to be sure all of the contacts are seating correctly and don't have a high voltage drop. At this point, you can also use a long jumper wire to connect the sender body to the battery negative, and sweep the sender to make sure it operates the daash gauge correctly.

If everything to this point tests OK, the only possibility left is a poor ground connection between the sender and the vehicle chassis. Use your DVOM to measure resistance in the ground circuit; you will probably find a poor electrical ground path adding resistance to the gauge circuit, raising resistance out of the operational range of the gauge. Clean and tighten all ground points between the fuel tank and the battery...

I hope this is helpful; if so, an accept would be most appreciated! Thanks!