when your car is braking using the ACC , and not the foot brake , of course it uses the brake light. This is the established rule for all car constructors and without it that are not able to install the ACC on cars. Imagine that the ACC can brake very fast and a big Truck from the back just will not observe it, especially during the night. I've even installed on my VW additional Off Road LED Spotlights. I know that it looks ugly on Arteon but I wanna have a good light because it increases the safety on the road.