How do brake lights activate in an air brake system?

In an air brake system, brake lights activate through a mechanism that involves air pressure working in conjunction with an electric switch. When the driver applies the brakes, the air pressure in the braking system is engaged, which then activates an electric switch. This switch sends a signal to the brake lights to illuminate, alerting others on the road that the vehicle is slowing down or stopping. This interaction is crucial for safety, as it communicates to other drivers that the vehicle is reducing speed, preventing potential collisions.

The function of brake lights is not dependent on the vehicle's speed, nor is it managed manually by the driver through a separate lever or control. Rather, it is an automatic response to the application of the brakes via air pressure, ensuring a reliable and consistent communication signal to others on the road. Hence, the correct answer reflects how modern air brake systems efficiently integrate air pressure with electrical components to maintain safety.