[19Fordy]

The hot wire from the gauge attaches to the single screw on top of the sender.
Then, to make sure the sending unit has a good ground, run a separate wire from one of the 6 screws that fasten the sending unit to the tank- to the frame of the car. Make sure the metal is very clean at the point of contact. I am assuming that your gauge panel is also grounded.
Report back your findings.

Another way to test your sending unit is to lay it on the rubber trunk mat and attach the hot wire to the sending unit. Then attach another wire with alligator clips from one of the screw holes in the unit to a part of the car that is grounded like the floor trunk latch. Then move the float by hand thru it's range of motion (with the key on) to see if the gauge registers. Your float might be bad and full of gas because of a crack. You can solder it or buy a new float.

If it still doesn't work, gently pry off the top of the sending unit and see if there is a problem. The little star wheel is used to adjust the gauge reading. CW makes gauge read closer to the Full mark. CCW makes it move closer to the Empty mark.