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Control Switch & Circuit Test

WARNING: On models with air bag, observe the following precautions. Disconnect negative and then positive battery cables. Shield both cables. Air bag system contains a back-up power supply built into the air bag diagnostic monitor. Wait a minimum of one minute before servicing any air bag system components. System is now disabled. See AIR BAG RESTRAINT SYSTEM article.
NOTE: Horn and/or cruise control may operate intermittently if ground brush is missing.
  1. Press brake pedal. Go to next step if stoplights operate properly. If stoplights do not operate properly, repair as necessary.
  2. Attempt to sound horn. Go to next step if horn operates properly. If horn does not operate properly, repair as necessary. See HORN RELAY CIRCUIT TEST.
  3. Locate 6-pin connector at amplifier. See AMPLIFIER LOCATION table under REMOVAL & INSTALLATION. Using DVOM, check for continuity between ground and circuit No. 57 (Black wire) on vehicles with analog cluster or circuit No. 397 (Black/White wire) on Aerostar with electronic cluster. Repair amplifier ground circuit if necessary. If ground circuit is okay, go to next step.
  4. Turn ignition on. Check for battery voltage at circuit No. 296 (White/Purple wire) on Aerostar, or circuit No. 302 (Dark Blue wire) on Explorer and Ranger. If battery voltage is present, go to next step. If battery voltage is not present, check fuse and wiring back to fuse panel.
  5. Press brake pedal. Check for battery voltage at circuit No. 511 (Light Green wire) on Explorer and Ranger, or circuit No. 810 (Red/Light Green wire) on Aerostar. If battery voltage exists, go to next step. If battery voltage does not exist, check wiring for continuity between brakelight switch and amplifier. If continuity does not exist, repair as necessary. If continuity exists between brakelight switch and amplifier, substitute known good amplifier. Replace amplifier if defective.
  6. Measure voltage at circuit No. 151 (Light Blue/Black wire). If meter indicates approximately 7.8 volts, go to next step. If meter indicates approximately 12 volts, service sticking speed control ON button or short to ground on circuit No. 151 (Light Blue/Black wire). If voltage is approximately zero, service shorted clockspring on Aerostar. If circuit No. 151 (Light Blue/Black wire) and ON-OFF buttons are both okay, substitute known good amplifier and repeat test.
  7. Measure voltage at circuit No. 151 (Light Blue/Black wire) while turning steering wheel 1/4 turn left and right with specified control switch pressed. See CONTROL SWITCH VOLTAGE table.
    CONTROL SWITCH VOLTAGE

    Switch Position Approximate Voltage
    No Button Pressed 7.8
    ON 12.0
    OFF 0
    RESUME 6.5
    SET-ACCEL 4.5
    COAST 1.5
  8. If voltages are as specified, cruise control switches are operating properly. Go to step 15). If voltages fluctuate or are not as specified, go to next step.
  9. Turn ignition off. Unplug 6-pin connector at amplifier. Measure resistance between circuit No. 151 (Light Blue/Black wire) and amplifier ground with specified switch pressed while turning steering wheel 1/4 turn left and right. See CONTROL SWITCH RESISTANCE table. If values are as specified, replace amplifier and retest. If values are not as specified, go to next step.
    CONTROL SWITCH RESISTANCE

    Switch Position Ohms
    OFF 0-1
    SET-ACCEL 646-714
    COAST 114-126
    RESUME 2090-2310
  10. Remove horn pad or air bag module (if equipped). Unplug 6-pin horn pad connector from steering wheel. Connect ohmmeter between circuits No. 151 (Light Blue/Black wire) and No. 6 (Dark Blue wire) on horn pad connector for Ranger and Explorer (Black lead on Aerostar).
  11. Press ON button. If resistance is greater than one ohm, replace cruise control switch assembly. If resistance is okay, connect ohmmeter between circuits No. 151 (Light Blue/Black wire) and No. 57 (Black wire) on horn pad connector for Ranger and Explorer (Black lead on Aerostar). Check for resistances specified in CONTROL SWITCH RESISTANCE table.
  12. If resistances are not as specified, replace speed control switch assembly. If resistances are as specified, remove steering wheel. Check circuits No. 151 (Light Blue/Black wire) and No. 57 (Black wire) for continuity between 6-pin connector and brush assembly (Explorer and Ranger) or clockspring (Aerostar). If continuity exists, go to step 14).
  13. If continuity does not exist, check for continuity between 3-pin brush connector and brush assembly. Also check for continuity of each wire between 3-pin connector and amplifier 6-pin connector. Repair wiring or replace brush assembly as required.
  14. If continuity exists on both circuits, clean brush assembly on Explorer and Ranger (clockspring assembly on Aerostar) with solvent, then lubricate with Speed Control Slip Ring Grease (ESA-M1C122-A). Reinstall steering wheel and horn pad.
  15. Measure resistance between circuits No. 150 (Green/White wire) and No. 397 (Black/White wire) on Aerostar, or between circuits No. 563 (Orange/Yellow wire) and No. 397 (Black/White wire) on Explorer and Ranger. If resistance is not 180-250 ohms, check for continuity between 6-pin amplifier connector and 2-pin speed sensor connector. If wiring is okay, perform SPEED SENSOR TEST (Explorer and Ranger) or REAR ANTI-LOCK SENSOR TEST (Aerostar).
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