[19Fordy]

Disconnect you battery so that only the dry cell power is feeding your gauge.
Connect the wire from the + terminal of your dry cell to the correct (input) terminal on your gauge.
Then connect a wire from the other gauge terminal to the screw on the top of your sending unit.
Then connect another wire from the negative terminal of your dry cell to the metal flange where the screw holes are on the gas tank sending unit.
Make sure all the connections are made on clean metal and make sure that your sending unit is resting on a piece of insulation material like a piece of cardboard.
When you do this your gauge should work.

Electricity is not my strong point but, I think you should make sure your gauge is isolated and not grounded to your battery. Use only the wiring shown in the sketch.

Perhaps another Fordbarner will chime in.