New sender unit. 3 wires from harness and ground from tail-lights that work. Black wires are to screw on periphery of circle. The other two are to the major “tangs” on sender. One way shows empty and other switch shows full even with 9 US gallons onboard. Have switched wires and either full tank or empty. One other tang on sender free and not occupied. Help. Thankx!! Bob
Have you tried reversing the direction that you inserted the sender into the tank? I initially inserted mine with the float device pointing towards the front of the car and had an erroneous reading on the gauge. after reversing it the fuel gauge read correctly.
The sender harness should have a green/black wire from the gauge, a white/green to the low level light in the speedo and a black ground. Not sure what sender you have but try connecting the black ground to the third blade. If you pull the sender to check the float orientation, test before reinstalling to confirm it works.
Sender wire with the float on it could be hung up in the internal baffle in the tank.
Can you check resistance?
One will be open circuit as it is for the warning light and will only turn to zero resistance when the fuel is low.
The other should be (I might be wrong) 23 Ohms full and 230 Ohms empty (or vice versa!)