What activates the spring-applied brake in the parking brake system?

The activation of the spring-applied brake in the parking brake system is achieved through the push-pull switch. This switch is designed to mechanically engage the braking system when pulled or pushed, providing a reliable means of activating the brake. The use of a push-pull mechanism helps ensure that the brakes are applied consistently and securely, allowing for safe parking of the equipment.

The other options do not serve this specific purpose: a hydraulic signal is typically associated with other braking systems rather than the parking brake, while the red light indicator merely serves as a visual alert to the operator without activating the brake itself. A manual lever could be involved in some systems but does not represent the mechanism specifically designed for activating the spring-applied braking system in this context. Hence, the push-pull switch is the critical component for engaging the parking brake effectively.