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Rear Window Does Not Defog

  1. Turn ignition off. Check fuse No. 29 (30-amp) in Central Junction Box (CJB) under left side of dash. If fuse is good, go to step  5 . If fuse is faulty, turn off ignition and replace fuse. If fuse fails again, go to next step.
  2. Turn ignition off. Disconnect CJB connector C368 and rear window defogger grid 1-pin connector C1891a. Measure resistance between ground and rear window defogger grid connector C1891a (Green/Blue wire). If resistance is greater than 10 k/ohms, go to next step. If resistance is less than 10 k/ohms, repair short to ground in Green/Blue wire between rear window defogger grid and CJB. See WIRING DIAGRAMS  . Recheck system operation.
  3. Disconnect CJB 10-pin connector C364 and rear window defogger switch 8-pin connector C437. Measure resistance between ground and rear window defogger switch harness connector terminal No. 6 (Green/Red wire). If resistance is greater than 10 k/ohms, go to next step. If resistance is less than 10 k/ohms, repair short to ground in Green/Red wire between rear window defogger switch and CJB. See WIRING DIAGRAMS  . Recheck system operation.
  4. Connect CJB connectors C368 and C364. Measure resistance between ground and rear window defogger grid 1-pin connector C1891b (Black wire). Measure resistance between ground and rear window defogger switch connector C437 terminal No. 6 (Green/Red wire). If either resistance is less than 10 k/ohms, replace CJB. Recheck system operation. If both resistances are greater than 10 k/ohms, problem may be intermittent. Recheck system operation.
  5. Turn ignition off. Disconnect CJB 2-pin connector C370. Turn ignition switch to RUN position. Measure voltage between ground and CJB 2-pin connector C370 terminal No. 1 (Red wire). If voltage is 10 volts or greater, go to next step. If voltage is less than 10 volts, repair open in Red wire between CJB and Battery Junction Box (BJB) as necessary. Recheck system operation.
  6. Turn ignition off. Connect CJB connector C370. Remove rear window defogger relay. Turn ignition switch to RUN position. Individually measure voltage between ground and rear window defogger relay 5-pin connector C56 terminals No. 2 and 3. See Fig 1 . If voltage is 10 volts or greater at both terminals, go to next step. If voltage is less than 10 volts exists at either terminal, replace CJB and recheck system operation.
  7. Turn ignition off. Remove rear window defogger relay. Test rear window defogger relay. See REAR WINDOW DEFOGGER RELAY  under COMPONENT TESTS. If rear window defogger relay is okay, go to next step. If rear window defogger relay is not okay, install NEW rear window defogger relay. Recheck system operation.
  8. Test rear window defogger switch. See REAR WINDOW DEFOGGER SWITCH  under COMPONENT TESTS. If switch is okay, go to next step. If switch is not okay, replace switch and recheck system operation.
  9. Using an ohmmeter, measure resistance of Black wire between ground and rear window defogger switch connector C437 terminal No. 2. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open Black wire between ground and rear window defogger switch as necessary. See WIRING DIAGRAMS  . Recheck system operation.
  10. Turn ignition off. Disconnect Central Timer Module (CTM) 20-pin connector C23 located on CJB. Install defogger relay. Turn ignition switch to RUN position. Measure voltage between CTM connector C23 terminal No. 12 and ground. See Fig 2 . Measure voltage between CTM connector C23 terminal No. 18 and ground. If voltage is 10 volts or greater at either terminal, go to next step. If voltage is less than 10 volts at one or both terminals, replace CJB. Recheck system operation.
  11. Turn ignition off. Disconnect CJB 10-pin connector C364. Measure resistance in Black/White wire between CJB terminal No. 5 and rear window defogger switch connector C437 terminal No. 1. See Fig 3 and Fig 4 . If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open in Black/White wire between rear window defogger switch and CJB. See WIRING DIAGRAMS  . Recheck system operation.
  12. Disconnect CTM 20-pin connector C23. Measure resistance in Black/White wire between CJB terminal No. 5 and CTM terminal No. 4. SeeFig 2 and Fig 4 . Measure resistance between CTM connector C23 terminal No. 5 and ground. Resistance should be less than 5 ohms between CJB and CTM and greater than 10 k/ohms between CJB terminal No. 5 and ground. If resistance is as specified, go to next step. If resistance is not as specified, replace CJB and recheck system operation.
  13. Disconnect rear window defogger grid 1-pin connector C1891b (Black wire). Measure resistance between ground and rear window defogger grid connector C1891b (Black wire). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open in Black wire between rear window defogger grid and ground. See WIRING DIAGRAMS  . Recheck system operation.
  14. Reconnect CJB 10-pin connector C364 and CTM connector C23. Disconnect rear window defogger grid connector C1891a (Green/Blue wire). Turn ignition and rear window defogger on. Measure voltage between ground and rear window defogger grid connector C1891a (Green/Blue wire). If voltage is greater than 10 volts, check defogger grid. See GRID FILAMENT TEST  under COMPONENT TESTS. Repair rear window defogger grid as necessary and recheck system operation. If voltage is less than 10 volts, repair Green/Blue wire and recheck system operation. See WIRING DIAGRAMS  .
Fig 1: Identifying Rear Window Defogger Relay Connector Terminals
G99F54887Courtesy of FORD MOTOR CO.
Fig 2: Identifying Central Timer Module (CTM) 20-Pin Connector Terminals
G98E03538Courtesy of FORD MOTOR CO.
Fig 3: Identifying Rear Window Defogger Switch 8-Pin Connector Terminals
G99H54889Courtesy of FORD MOTOR CO.
Fig 4: Identifying Central Junction Box (CJB) 10-Pin Connector Terminals
G98G03539Courtesy of FORD MOTOR CO.
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