What activates the stop switch?

What activates the stop switch?

• A. Brake pedal
• B. Air pressure
• C. Engine oil pressure
• D. Fuel level

Answer: (B)

Air pressure controls the stop switch. In many air-brake systems, the stop switch is wired to monitor the air supply; when pressure falls to a safe minimum, the switch activates to stop the engine or prevent the vehicle from continuing to operate, to avoid losing braking power. So air pressure is the trigger for this safety device.

The brake pedal is what you press to apply the brakes, but it doesn’t trigger the stop switch itself. Engine oil pressure relates to lubrication and engine health, not the stop switch. Fuel level doesn’t regulate the stop switch either.