60mm Defi-Link Meter BFs are electronic blacked out gauges which are high response and refined design. When the car is off they have a black face with no numbers on them. As soon as the car is turned on, the gauges light up and are in full affect. Defi-Link Meter BFs need to be connected to Defi-Link Control Unit II. Up to 6 gauges can be connected and controlled by one Control Unit II. The name of the connection system is "Defi-Link System." Defi-Link System allows gauges to be attached to Defi-Link Control Unit II with a single "DAISY CHAIN" wiring system.