The gauge will have an ignition terminal (switched 12V) and a sender terminal and I believe is grounded by the case/mounting. The sender should be also grounded from one of it's mounting screws to the frame. This is a must have wire, otherwise you are relying on straps, tubing or touching, not good. Wire brush the sender flange, screw and a nearby spot on the frame, install the wire and then cover all the bare spots with that liquid insulator. Be sure the frame is grounded to the body and body to engine. It all should be checked for operation before final installation. The same careful grounding should be done at the gauge(s).
