what spare said!
On the gauge you will have (or at least the old gauges) a pigtail for the light (connected thru the navigation lights switch), Terminal "I" for the hot (positive from either the engine or instrument cluster via the fuse panel, usually a red wire), Terminal "G" is the ground (you will have 2 wires on this terminal, one to the sender and the other from the ground of the instrument cluster, usually a black wire), And Terminal "S" to the sender (usually an identified wire, of no particular color)