Cruise Control (Tempostat) Operation and Troubleshooting

How the Tempostat works

The automatic cruise control — the factory calls it the Tempostat — holds the road speed you set with the steering-column operating switch. A control unit watches the car's speed signal and drives a throttle actuator (a small motor with a feedback potentiometer) through a Bowden cable to the throttle linkage, opening and closing the throttle to keep the set speed.

The control unit cancels cruise the instant you ask it to:

• Brake — the brake-light circuit grounds a control-unit terminal through the brake-light bulb filaments. When you press the pedal that ground is removed and cruise drops out. Because cruise borrows ground through the bulbs, it also shares the brake-light fuse.
• Clutch — a clutch switch opens when the pedal is pressed, telling the control unit to release the throttle.

The operating switch on the steering column carries the On/Accelerate, Resume, and Off functions (the earliest cars use a Memory button instead of Resume).

Choose your car

The cruise-control circuit, fuse, and connector layout changed partway through the 1985 model year. Pick the configuration that matches your car for the dedicated troubleshooting guide.

• Early cars (up to model year 1985½) — fuse 8, a single control-unit connector, road speed taken from a pulse generator at the left front wheel.
• Later cars (model year 1985½ onward) — fuse 19, two control-unit connectors (instrument and front-end), road speed taken from the speedometer signal.