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 MANUALSMERCURY1994COUGAR 3.8 4, 4R70WREPAIR AND DIAGNOSISACCESSORIES & EQUIPMENTHEATED GLASS/DEFOGGERSDEFOGGER - REAR WINDOWTESTINGGRID FILAMENT TEST
1994 Mercury Cougar 3.8 4, 4R70W
Grid Filament Test
1994 Mercury Cougar 3.8 4, 4R70WSECTION Grid Filament Test
- Shine a strong light through grid from inside vehicle. Inspect grid from outside. Broken grid lines will appear as brown spots. Run engine at idle. Turn defogger on. Indicator light should come on.
- Connect negative lead of a voltmeter to ground. Touch positive lead to wide Red-Brown strips on rear window. Meter should indicate 10-13 volts. If voltage is lower, window grid ground wire (pigtail) connection is loose. Contact a known good ground. Reading should not change.
- With voltmeter negative lead grounded, touch voltmeter probe to each grid line at its midpoint. A reading of about 6 volts indicates grid line is good. A zero reading indicates grid line is broken between midpoint and battery side of grid. A 12-volt reading indicates grid line is broken between midpoint and ground.
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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.