Grid Filament Test

1995 Mercury Cougar 3.8 4, _NA_SECTION Grid Filament Test
  1. 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.
  2. 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 wire (pigtail) connection is loose.
  3. 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. If voltmeter reads 12 volts or zero volts, grid line has a break.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.