Filament Inspection

Turn the ignition switch to the ON position.
Turn the rear window defroster switch on.
CAUTION:
- Directly touching the rear window defroster filament with the lead of the tester could damage it. Wrap aluminum foil around the end of the lead and inspect the filament by touching it with the foil.
Fig 1: Checking Filament For Breaks
Courtesy of MAZDA MOTORS CORP.
Connect the positive lead of the tester to the positive side of each filament and the negative lead to ground.

Gradually slide the positive lead from the positive side to the negative side and verify that the voltage decreases accordingly.

If the voltage changes rapidly, the filament has a malfunction. Repair the filament.

FILAMENT VOLTAGE SPECIFICATIONS

Measured part	Voltage (Reference)
(1) to (2)	Approx. 12 V to 0 V

Fig 2: Measuring Filament Voltage

Courtesy of MAZDA MOTORS CORP.