Rear Window Defogger Filament Check
Filament Check1. Attach probe circuit tester (in volt range) to middle portion of each filament.
2. If a filament is burned out, circuit tester registers 0 or 12 volts.
3. To locate burned out point, move probe to left and right along filament. Test needle will swing abruptly when probe passes the point.
When measuring voltage, wrap tin foil around the top of the negative probe. Then press the foil against the wire with your finger.