When Does Radar Cruise Control turn on the brake lights?

Sometimes the cruise control just relaxes the throttle to slow the car.

Other times it applies the brakes. And the brakes play by the same rules whether you or the radar is on the pedal, so the stop lamps come on.

 

Yep, as mentioned, when it slows hard enough it turns on the brake lights. I've had at least one occasion where it was the right amount of dark so I could see when the brake lights were coming on while driving.

If you really wanted to see it though it seems you'd pretty much have to either tap a brake light wire so you could run it to a light up front, etc... Or maybe you could somehow mount a mirror on the back of your car? Or maybe mount a camera back there? Nothing that seems super duper easy...

 

My 1959 VW had that. All the other lights dimmed a certain amount when the stop lamps were on. You got used to it.

 

I tested the brake lights in my 2012 plug in and the the brake lights came on satisfactorily during cruise control braking. I had installed a tow hitch and pierced the wiring for the lights but it was a several hour job to find and connect the right wires. After I had the wiring on place I managed to feed the connector around the back seat and plugged in a cheap test adapter with lights (Harbor Freight) so I could monitor it in the mirror.

 

It also had the VW included option of generator functionality
rev the motor at idle to check charging system was operating