Yes the original sstem was 6v converted to twelve at some point with a drop down for the gauges. With the fuel gauge wired thru the dropping resistor , I checked the sending unit wire for power because the gauge wasn't working. At that point the testor light would flash and the gauge wasn't registering anything.... why was the testor light flashing?
I rewired the fuel gauge making it 12 v. and disconnected the wire that took went from other side of gauge to the rest of the gauges so it was not sending 12v to the rest of the gauges and made them run off the drop down. So now I only have 12v to the fuel gauge. The other wire from the fuel gauge is the sender wire, as the gauge is grounded.
Wired that way when the key is on the gauge goes to full. If I understand you Doc , I should wire a Linear taper potentiometer somewhere along the sender wire. Correct?