Which component is crucial for activating the stoplight switch?

The dual control foot valve is crucial for activating the stoplight switch. This component is connected to the brake pedal and is responsible for controlling the air supply to the brake system when the driver applies the brakes. When the foot valve is actuated by pressing the brake pedal, it allows air to flow through the system, simultaneously sending a signal to activate the stoplight switch. This action ensures that the brake lights illuminate while the brakes are applied, alerting other drivers of the bus's intention to stop.

In a typical brake system, the other components do not directly impact the activation of the stoplight switch. The air compressor generates the air pressure needed for braking but does not interact with the stoplight switch directly. The two-way check valve is designed to prevent backflow within the system and does not play a role in activating the lights. The safety valve is crucial for maintaining system pressure and preventing overpressure situations, but it also does not influence the functionality of the stoplight switch. Thus, the dual control foot valve is the essential component that facilitates the activation of the stoplight system when brakes are applied.