This switch is mounted on the pedal assembly and is used to send the status of the brake pedal to the HECU.

The switch is turned on when the brake pedal is pressed. The brake light switch is a normally-open contact type which runs to battery voltage when it is active (this means that the brake pedal is pressed). When it is passive (this means that the brake pedal is released), the line is grounded via the brake light bulb.