12 For wiring, you'll need a couple of feet of 18-gauge wire in a few primary colors. We used red for power, black for ground, and yellow for gauge illumination. On the back of each gauge, are several 8-32 threaded studs. You'll install the power wire to the I terminal, the ground wire to the G terminal, and the illumination wire goes to the male spade terminal next to the bulb itself. Nothing should be connected to the O terminal and the S terminal is where your in-dash sending unit wires will eventually be connected.