Both of my gauges use a +12V to dim and then backlight the gauge. Aka, its normal/bright, then when I turn on headlights, they dim and backlight themselves. I dug around in the control cluster for the right wires, got fed up, and since I already had the center console apart, tapped into the lighting circuit that goes around the cigarette lighter. I'm not sure if that circuit dims, but it definitely works for headlight ON/OFF without hacking up that cramped cluster of wires behind the control cluster.