How is it not working? Pick a number.
Problems:
1. Will not hold proper speed
2. Cruise intermittently cuts out
3. Vehicle surges
4. Cruise control inoperative
Possible causes:
1. Incorrect cable adjustment; Binding throttle linkage; Leaking vacuum servo diaphragm; Leaking vacuum tank; Faulty vacuum or vent valve; Faulty stepper motor; Faulty transducer; Faulty speed sensor; Faulty cruise control module
2. Clutch or brake switch adjustment too tight; Short or open in the cruise control circuit; Faulty transducer; Faulty cruise control module
3. Kinked speedometer cable or casing; Binding throttle linkage; Faulty speed sensor; Faulty cruise control module
4. Blown fuse; Short or open in the cruise control circuit; Faulty brake or clutch switch; Leaking vacuum circuit; Faulty cruise control switch; Faulty stepper motor; Faulty transducer; Faulty speed sensor; Faulty cruise control module
That's the cruise control troubleshooting chart from my 83-90 Chilton's manual. Hope it helps.