Diode Dynamics 4th Brake Light Module | 2015+ Ford Mustang (DD3017)Red Running Light: The red light comes on at 50% brightness anytime you have your parking lights or headlights on, to serve as a rear fog lamp. This provides a distinct appearance at night, complementing the factory LED tail lights. 4th Brake Light: When you hit the brakes, the red light powers at full brightness, to serve as a supplementary brake light, for greater visibility and a unique look. White Reverse Light: Anytime you're in reverse, the red