Brake Light Switch: Description and Operation

Brake Lamp Switch
The Brake Lamp Switch signals the Powertrain Control Module (PCM) with a battery positive voltage (B+) signal whenever the vehicle brake pedal is applied.

The signal informs the PCM to disengage the torque converter clutch, speed control and auxiliary idle control (if equipped).

If all the stoplamp bulbs are burned out (open), a high voltage is present at the PCM due to a pull-up resistor in the PCM. This provides fail-safe operation in the event the circuit to the Brake Lamp switch has failed.