What does the governor control in a vehicle's air brake system?

The governor in a vehicle's air brake system is responsible for controlling when the air compressor pumps air into the air storage tanks. It manages the air pressure levels in the system to ensure that there is adequate air supply for braking. When the pressure in the tanks drops below a certain threshold, the governor activates the compressor to replenish air, thus maintaining the necessary pressure for safe and effective braking.

Understanding the role of the governor is crucial for maintaining a properly functioning air brake system, as it helps prevent pressure loss that could lead to brake failure. The other options provided do not accurately represent the governor's function; for instance, the power supply to the brake lights is unrelated to the governor, and the timing of brake pad replacement and adjustment of brake pressure are managed through different mechanisms in the braking system rather than directly by the governor itself.