Secondary braking systems must include which control feature?

• A. A switch to turn them off
• B. Automatic engagement only
• C. Pressure relief valve
• D. Manual brake lock

Answer: (A)

Secondary braking systems are there to provide an extra level of stopping power, but a driver must have a clear way to disable them when needed. A switch to turn them off gives a deliberate, user-controlled override so the operator can rely on the primary brakes during normal driving, set up or maintenance, or perform tests without the secondary system engaging unexpectedly. This control prevents unwanted braking forces that could surprise the driver or affect vehicle stability, especially on grades or when precise positioning is required. The other possibilities don’t provide this essential control: automatic engagement removes the driver’s ability to disengage when needed, a pressure relief valve is a hydraulic safety component rather than a user control to deactivate the system, and a manual brake lock creates a fixed condition that could render the vehicle uncontrollable if engaged unintentionally.