told me it was designed for 12V lights on for dimming. It has dimming built in so I can adjust that via the gauge settings to match whatever I set the stock interior lighting at. It would be nice to be able to adjust dimming via the stock system, but not necessary. So once I set the dimmer built into the gauge, I'm assuming every time I turn on the 12V source via the headlight switch it will go to the dimmer setting I program into the gauge.