"The sending unit was hooked up directly to the hot side on the fuel gauge. Power came directly from a 12v battery through a voltage reducer, to the power side of the fuel gauge"
again, the sender provides the ground that makes the gauge work, it is not/can't be hooked to the "hot" side, which is what would be the battery or positive side - the only way the sender would be damaged is maybe if you run a full 12V thru it to ground it might fry the resistance in it - when testing just don't make 'permanent' connections, have the battery + wire in hand and just touch it to the post to watch the reaction
what are you calling the "ground connection on the sending unit"? the sender is grounded by it's mounting flange screws, the wire terminal on the sender is the wire to the gauge .... the circuit is >
battery + to the + terminal on the gauge;
battery - to the gauge case and sender case;
sender terminal to the 2nd terminal on the gauge
someone else might have a better idea of why a gauge would work backwards, but to me if it reads backward, the wires are on backward
Bill
