Which system controls the brake lights in an air brake system?

The vehicle's electrical system is responsible for controlling the brake lights in an air brake system. When the brake pedal is pressed, the electrical signals are activated to illuminate the brake lights, indicating to other drivers that the vehicle is slowing down or stopping. This system operates independently of the air brake components, which are primarily focused on the braking function itself rather than the signaling function.

In an air brake system, while components like the main air pressure regulator and air compressor are vital for the operation of the brakes—ensuring that sufficient air pressure is maintained to apply the brakes—the actual lighting for the brake signals is managed through the vehicle's wiring and electrical components. The parking brake is also a critical part of the braking system, but it primarily engages the brakes to hold the vehicle stationary rather than controlling the brake lights. Thus, the correct answer identifies the source that regulates the signaling aspect, which is essential for safe driving.