Cruise Control Systems: Operation

The control unit gets input from the speed pick-up coil and feeds a signal to the throttle actuator. A memory circuit allows the control unit to bring the car back up to a chosen speed after the brakes have been applied.

The system has 3 or 4 safety switches, depending on the transmission used in the vehicle. The brake switch (if equipped) opens the circuit that shuts off the system when either pedal is depressed.

At the same time, a vacuum valve on the brake pedal bracket opens and vents throttle actuator vacuum. If none of these switches work, a mercury retard switch will open when the car slows, stopping cruise control operation.