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Wiring the MTX-L is a simple three-wire proposition (12V power, ground, and headlight power). The only thing to be mindful of during this step is to tap the white wire into the headlights’ power source and not the dimmer. A rheostat switch like a Mustang’s dimmer will cause the gauge to malfunction. You’ll also see a yellow wire in the harness, which is used for sending analog data from the gauge to an aftermarket/standalone PCM (in closed loop) or a datalogger.