Brake light switch

Two switches are built into the brake-light switch: the brake-light switch and the brake-light test switch (redundancy for safety reasons). The signals indicate to the DME control module whether the brake pedal has been pressed.

Fig 1: Identifying Brake Light Switch And 4-Pin Plug-In Connection

Courtesy of BMW OF NORTH AMERICA, INC.

The brake-light switch is supplied with 12 Volts, terminal R, and ground. Two signal lines lead into the DME. When the brake pedal is not pressed, the clutch module delivers 0 Volts across a signal line to the DME, and when the brake pedal is pressed it delivers 12 Volts. The brake light test switch delivers the same signals to the DME.