Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMERCURY1999SABLE LS, 4D SEDAN, 3.0 SREPAIR AND DIAGNOSISACCESSORIES & EQUIPMENTHEATED GLASS/DEFOGGERSREAR WINDOW DEFOGGER SYSTEMDIAGNOSTIC TROUBLE CODE (DTC) TESTSDTC B1347: DEFOGGER RELAY OUTPUT CIRCUIT FAULT
1999 Mercury Sable LS, 4D Sedan, 3.0 S
DTC B1347: Defogger Relay Output Circuit Fault
1999 Mercury Sable LS, 4D Sedan, 3.0 SSECTION DTC B1347: Defogger Relay Output Circuit Fault
- Turn ignition switch to RUN position. Press rear window defogger switch. Measure voltage between ground and defogger grid connector (Brown/Light Blue wire). If battery voltage exists, go to next step. If battery voltage does not exist, go to step 4 .
- Turn ignition off. Remove rear window defogger relay. Measure resistance between ground and rear window defogger relay connector terminal No. 85. See Fig 1 . If resistance is less than 10,000 ohms, go to next step. If resistance is greater than 10,000 ohms, replace rear window defogger relay.
- Disconnect Generic Electronic Module (GEM) 19-pin harness connector, located below fuse junction panel. Measure resistance between ground and rear window defogger relay connector terminal No. 85. See Fig 1 . If resistance is less than 10,000 ohms, replace interior fuse panel. If resistance is greater than 10,000 ohms, replace GEM. Restore electrical connections and recheck for DTCs.
- Turn ignition off. Remove rear window defogger relay. Turn ignition switch to RUN position. Measure voltage between ground and rear defogger relay connector terminal No. 86. See Fig 1 . If battery voltage exists, go to step 6 . If battery voltage does not exist, go to next step.
- Brake shift interlock is powered by same fuse as defogger relay (fuse No. 5). Turn ignition switch to RUN position. Press brake pedal. Shift transmission from Park to any other gear. If gear selector shifts out of Park, replace interior fuse panel. Recheck system operation. If gear selector does not shift out of Park, check fuse No. 5 and replace if necessary. If fuse is good, repair Red/Light Blue wire between ignition switch and fuse panel. See WIRING DIAGRAMS . After repair, recheck system operation.
- Turn ignition off. Reinstall rear window defogger relay. Disconnect 16-pin connector from GEM. Turn ignition switch to RUN position. Check for battery voltage at pin No. 16. If battery voltage exists, replace GEM. If battery voltage does not exist, go to next step.
- Turn ignition off. Remove rear defogger relay. Measure resistance between rear window defogger relay pin No. 85 and fuse junction panel connector terminal No. 16. See Fig 1 . See WIRING DIAGRAMS . If resistance is 5 ohms or less, replace rear window defogger relay. If resistance is greater than 5 ohms, replace fuse junction panel. After repair, recheck system operation.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.