Air Brake Practice Test 2026 – All-in-One Resource to Master Your Certification!

In an air brake system, the electrical stop light switch is controlled by air pressure. When the driver applies the brakes, air pressure is generated in the system. This pressure activates the stop light switch, signaling to the brake lights to illuminate and alert other drivers that the vehicle is slowing down or stopping. This functionality is crucial for safety on the road, as it ensures that the operator of a following vehicle is warned of decelerating or stopping.

Air pressure control is particularly integral in air brake systems because these systems rely on compressed air rather than hydraulic fluid to operate the brakes. This creates a more immediate and reliable response time in activating the stop lights in conjunction with the brakes. The other mechanisms, such as hydraulic pressure, driver input, or spring pressure, do not directly control the stop light switch in this context and focus on different aspects of the braking process.