Using Electronic Tester

Fig. 1 Speed Control Diagnosis Chart:

Fig. 2 Speed Control Wiring Circuit:

The most accurate method of fault tracing this speed control system requires the use of test unit, tool No. 9990943-4. This test unit will check the functions of all components including the control unit. Refer to Figs. 1 and 2 when testing this system.
1. Connect speed control tester as follows:
a. Remove underdash panel from driver's side.
b. Disconnect speed control harness from control unit.
c. Connect tester lead to the control unit.
d. Connect speed control wiring harness to tester unit.
2. Switch tester to position ``1.'' Turn ignition switch on, but do not start engine.
3. Check each switch position of the speed control system and compare as shown in Fig. 1.
4. If tester lamps do not light in the correct sequence, proceed as follows:
a. Check fuse No. 12 and wiring, Fig. 2.

Fig. 3 Speed Control Switch Wiring Circuit:

b. For ``Resume and Set'' lamps, check yellow and green wires between control unit and switch, Fig. 3. If not satisfactory, locate and repair open circuit in wires. If satisfactory, replace switch.
c. For ``Brake/Clutch'' lamp, check adjustment of switches on pedals. Check wiring and brake light operation. If not satisfactory, repair as necessary.
d. For the ``Speed'' lamp, verify proper operation of the speedometer. Check connection of orange wire at the rear of the instrument cluster. If not satisfactory, repair as necessary.
e. For ``Vac and Vent'' light, check three wires going to the servo valve under the hood. If not satisfactory, repair as necessary.
5. On vehicle less limited-slip differential, raise left rear wheel off the ground. Rotate wheel slowly while watching ``Speed'' light on tester. Light should blink on and off with low light intensity.
6. On vehicle with limited-slip differential, raise both rear wheels off the ground and set transmission to ``Neutral.'' Rotate wheels slowly while watching ``Speed'' light on tester. Light should blink on and off with low light intensity.
7. On all models, set speed control to the ``OFF'' position and start engine. Allow engine to run for approximately 30 seconds to establish vacuum.
8. Turn engine off, then turn ignition switch to ``ON'' and speed control to ``ON.'' Depress ``VAC'' and ``VENT'' buttons on the tester simultaneously. Throttle pedal should be pulled down. If throttle pedal is not pulled down, proceed as follows:
a. Release the ``VAC'' button on tester and keep ``VENT'' button depressed for a minimum of 15 seconds. Throttle pedal should remain steady. If not, the vacuum system has a leak. Repair as necessary.
b. If vacuum supply is satisfactory, replace control unit.