How To Obtain Stop Light Circuit for Brake Controller On a 2008 BMW 5 Series

Question:

Is there a minimum voltage from the cold side of the brake switch? My 08 535xi has 2 cold side wires from the brake switch. One has a 9v out put when the brake is depressed. This wire did not trigger the brake controller and the other one is a 12v wire and this one stopped working altogether after switching to it. What other alternative do i have to installing the red wire of the brake controller? Can i piggy back off of the brake light wire off of the curt 4 way trailer plug module?

asked by: Juan G

Expert Reply:

The stop light switch circuit for a brake controller will need to have a full 12 volts. If the stop light switch circuit on a 2008 BMW 5 Series does not have a full 12 volts or a signal cannot be obtained then the solution for you is to install the Roadmaster Universal Stop Light Switch Kit part # RM-751000 which has been used for this very same purpose in the past and also eliminates having to splice into any wires on the vehicle. There are certain vehicles like a BMW 5 Series in which there is just not a sufficient stop light switch circuit to splice into for a brake controller therefore an artificial stop light switch like the above must be used.

The stop light circuit for the taillights should not be used for the brake controller.

expert reply by: Conner L