Cruise Control: Description and Operation

When the ignition switch is in Accy or Run, voltage is applied to the cruise control switch. When the cruise control switch is on, voltage is applied to the cruise electronic control unit, the cruise mode switch, vacuum pump/vent valve, cruise vacuum pump electro valve and the cruise control safety relay. The cruise on indicator light is at full brightness.

If the vehicle speed input to the cruise electronic control unit from the vehicle speed transducer is above 24 mph, the cruise electronic control unit will ground to start the vacuum pump. The cruise vacuum pump electro-valve receives a ground from the cruise control safety relay and the stop lights. On vehicles equipped with manual transmissions, the clutch switch is connected in place of the cruise control safety relay. On all vehicles, the cruise vacuum pump electro-valve energizes and closes the vent to atmosphere.

If the cruise mode switch is moved to the Set/Accel position and then released, voltage is momentarily applied to the Set/Accel input of the cruise electronic control unit. then operates the vacuum pump vent valve to control the throttle actuator to maintain current vehicle speed.

If the cruise mode switch is held in the Set/Accel position, the vehicle will accelerate to a new speed. When the cruise mode switch is released, the new speed will be maintained. If the cruise control safety relay or clutch switch is opened, the cruise vacuum dump electro-valve is de-energized and vents any vacuum in the cruise system, disengaging the cruise system. If the brake pedal is applied, voltage is applied to the stop lights which removes the ground from the cruise coast input and disables the cruise electronic control unit. The cruise electronic control unit is also disabled when the cruise mode switch is moved to coast. In this case, an internal resistance in the cruise electronic control unit raises the cruise coast input to 12 volts.

When the cruise control system is disengaged, moving the cruise mode switch to Resume will apply voltage to the resume input and the vehicle will accelerate to the previously set speed.