Mazda RX-7 Rear Window Defoggers: relay, grid filaments and more

Mazda RX7 1993-1995 FD3S



Heating grid filament is bonded to inside of rear window. Defogger relay allows power to heating grid filament. Defogger timer maintains power to grid for 10 or 15 minutes or until ignition is turned off. Indicator light comes on when defogger is on.

ELECTRICAL COMPONENT LOCATIONS

• Defogger Relay: In Luggage Compartment, On Left Wall
• Defogger Timer: Defogger timer is an integral part of Central Processing Unit (CPU). CPU is attached to joint box at left kick panel.

ON-VEHICLE SERVICE

GRID FILAMENT REPAIR

1. If necessary, use razor blade or equivalent to remove small amount of silicone from damaged area to expose grid line. Clean exposed broken grid line area with alcohol. Place tape along both sides of grid line area to be repaired. See Fig. 1. If Brown filament is broken, apply Brown touch-up paint to Brown grid line break area (if necessary).
2. Apply Silver Touch-Up Paint (2835-77-600) over Brown touch-up paint at break area, overlapping both lines. Allow a few minute drying time before carefully removing tape from line edges. DO NOT touch repaired area for 24 hours.

Fig. 1: Repairing Defogger Grid Filament

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COMPONENT TESTING

PRELIMINARY CHECKS

Turn ignition on. Turn defogger switch to ON position. If glass is not warm after a few minutes, check fuse. DEFOG fuse is in main fuse box, located in engine compartment on inner fender. If fuse is okay, use a test light or voltmeter to check for battery voltage at grid feed wire. If battery voltage exists, check grid filament for good ground or breaks in grid wire filaments. Repair circuit(s) as necessary. If battery voltage does not exist, check defogger switch, defogger relay and wiring harness. If components are okay, replace defogger timer (if equipped).

DEFOGGER SWITCH

Disconnect defogger switch connector. Check continuity between specified terminals of defogger switch connector. See Fig. 2. With defogger switch in OFF position, continuity should not exist. With defogger switch in ON position, continuity should exist. If continuity is not as specified, replace defogger switch.

DEFOGGER SWITCH CONTINUITY TEST

• Protege and RX7: Terminals "C" and "D"

Fig. 2: Identifying Defogger Switch Connector Terminals

DEFOGGER RELAY

Remove defogger relay. Check continuity between defogger relay terminals "C" and "D". See Fig. 3. If continuity exists, replace defogger relay. If continuity does not exist, apply battery voltage across defogger relay terminals "A" and "B". Check continuity between defogger relay terminals "C" and "D". If continuity exists, defogger relay is okay. If continuity does not exist, replace defogger relay.

Fig. 3: Identifying Defogger Relay Terminals/Internal Circuit

GRID FILAMENT

1. To locate breaks in grid wire filaments, attach a voltmeter probe to middle portion of filament. See Fig. 4. Attach other voltmeter probe to vertical section of window grid.
2. If wire is not broken, voltmeter will register approximately one half of battery voltage. If a grid is broken, voltmeter will register zero volts or battery voltage, depending on whether grid is broken between test leads or outside test leads. To locate break, move probe along wire until voltmeter needle moves abruptly.

Fig. 4: Testing Grid Filaments




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Mazda RX7 1993-1995 FD3S

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