The AUTO PARK warning lamp turns on when the system pressure is less than 3 100 kPa (450 psi) or when the electric/hydraulic pump motor is running due to the pressure maintenance switch being closed. The pressure maintenance switch and the light switch supply B+ to the circuit for lamp operation. Releasing the parking brake causes the warning light switch to open the circuit and turn the lamp off. This lamp will flash at partial release pressures.

The parking brake pump assembly is located in a component box on the passenger side of the vehicle. The component box is on the inside of the right frame rail in front of the rear axle. It consists of an electric pump and a fluid reservoir. The pump provides fluid pressure to operate the system. A pressure relief valve in the pump limits system pressure to 12 400 kPa (1800 psi).

The pressure maintenance switch mounts to the parking brake pump assembly housing. It is a hydraulic pressure switch that operates within a certain pressure range, turning the pump motor on and off. The pressure maintenance switch closes when the system pressure is below 8 300 kPa (1200 psi) and opens when the system pressure reaches approximately 1100 kPa (1600 psi). The pressure maintenance switch applies B+ to the coil side (control side) of the relay switch.

The parking brake solenoid valve is a solenoid and valve assembly located in the component box on the underside of the vehicle. The solenoid controls when the fluid can return to the pump reservoir. When the parking brake is released, the valve closes to hold pressure in the system. When the parking brake is applied, the valve opens in order to allow the fluid to return to the pump reservoir.

The actuator is located in the component box on the underside of the vehicle. It is a spring-loaded device that operates the parking brake cable. A large spring inside the actuator applies the parking brake. When the fluid pressure against the piston is great enough, it overcomes the spring tension and pushes the piston to release the parking brake.

The cam-actuated switch is located to the left of the steering column intermediate shaft. It is a normally open switch that closes when the column shifter is moved out of the P (Park) position. B+ is applied to the solenoid valve and to the pressure maintenance switch when the cam-actuated switch is closed.

The parking brake relay is located in the component box underneath the vehicle. The relay receives B+ from the pressure maintenance switch and acts as the automatic control circuit for the high current required to run the pump motor. When the pressure maintenance switch supplied B+ to the relay switch, the contacts close to complete the feed circuit to the pump motor.

The parking brake light switch is a hydraulic on/off switch located in the component box underneath the vehicle. The light switch is mounted with a fitting on the back of the actuator assembly. The light switch controls the ground side of the AUTO PARK lamp. The lamp switch closes when the system pressure is below 3 100 kPa (450 psi), turning on the light when the ignition is ON.

The parking brake switch is a manual on/off switch on the instrument panel. The location is determined by the body builder. Pushing in the switch releases the parking brake. Pulling out the switch applies the parking brake.