On the GlowShift volt gauge there are three wires. The red wire controls the lights on the needle and dial as well as read the voltage that the alternator is putting out. The yellow wire is the memory wire for the colors and the black is ground. You must connect red to a 12- volt ignition switched voltage. The yellow wire needs to be connected to a 12-volt constant voltage, and the black wire needs to be connected to a good ground.