See Figures 1, 2, 3 and 4
Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades up or down may cause variations in the selected speeds. The electronic cruise control system has the capability to cruise, coast, resume speed, accelerate, "tap-up" and "tap-down".
The main parts of the cruise control system are the functional control switches, cruise control module servo, vacuum tank, switch assembly, vacuum hoses, wiring and cruise control servo cable.
The cruise control system works a mechanical linkage to the throttle by way of a vacuum motor which is inside a server. This is a diaphragm moved by vacuum applied to one side. A solenoid driven valve connects the vacuum motor to a vacuum tank. Another solenoid vents the vacuum. The cruise control module controls the servo and the throttle by pulsing these solenoid valves on and off.
One input to the cruise control module is the vehicle speed, which is sent to the computer control module (ECM or PCM, as applicable) by the Vehicle Speed Sensor (VSS). The cruise control module assembly contains a low speed limit which will prevent system engagement below 25 mph (40 km/h).
Other inputs to the module are the switches. The module is controlled by the functional switches in the turn signal/headlamp switch and windshield wiper lever. The release switches are mounted on the brake/clutch/accelerator pedal bracket. When the brake or clutch pedal is depressed, the cruise control system is electrically disengaged and the throttle is returned to the idle position.