One end of this small switch looks like a small button, and when it’s pressed the brake lights turn off. The button is pressed by the brake pedal unless the brake pedal is compressed. This creates the situation where the brake lights activate anytime the brakes are pressed. It’s easiest to consider the brake light switch to work the opposite of the brake pedal. When the pedal is pressed, the switch just isn’t, likewise, when the switch is pressed, the brake pedal is resting. This switch also sends a signal to the ignition switch and gear selector. The aim of this signal is to make sure the brake pedal is pressed before starting the vehicle, or moving the gear selector out of park.