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 MANUALSMERCURY1989GRAND MARQUIS LSREPAIR AND DIAGNOSISACCESSORIES & EQUIPMENTHEATED GLASS/DEFOGGERSDEFOGGER - REAR WINDOWTESTINGCONTROL ASSEMBLYALL OTHER MODELS
1989 Mercury Grand Marquis LS
All Other Models
1989 Mercury Grand Marquis LSSECTION All Other Models
- Ground pin No. 2 ("G") and connect a jumper wire between pins No. 3 ("I") and 4 ("B"). Connect a 12-volt test light between pin No. 1 ("L") and ground. Apply power to pin No. 4 ("B"). Test light should not glow. See Fig 1 . On Mark VII and Continental, apply power to pin "S". Heated rear window symbol should light.
- On all models, turn control switch to "ON" position. Test light should come on and stay on after switch returns to normal position. Test light should go off if control switch is turned to "OFF" position, jumper wire between pins No. 3 ("I") and 4 ("B") is removed, power to ignition switch "ACC" terminal is removed, or 10 minutes have elapsed.
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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.