Rear Hatch Defroster Troubleshooting and Repair
Electrical diagnosis procedure for the rear hatch defroster grid, covering voltage checks, relay bypass, grid tab reattachment, and grid line repair kits.
Auxiliary fuse box — early cars
| № | Rating | Protected circuit |
|---|---|---|
| 4 | 25 A | Rear-window defogger |
Central electric panel — later cars (1985.5+), by fuse number
| № | Rating | Protected circuit |
|---|---|---|
| 13 | 30 A | Rear-window defogger |
Numbered by official fuse number 1–41 (the late fuse list). The factory does not publish a 1:1 map between these numbers and the physical carrier positions, so this logical view is ordered by number; see the physical Type-2 carrier for the as-installed layout. Fuses 12, 26, 27, 29 and 35 are unpopulated.
Introduction
The rear hatch defroster grid functions as a large resistor. When operating correctly, a voltmeter will read +12 VDC on one side of the grid and 0 VDC (ground) on the other.
Tools
- Multimeter
- Spade connector jumper
Procedure
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Turn on the ignition and the defroster switch.
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Using the voltmeter function on the multimeter, connect the negative lead to a ground point and use the positive lead to check both sides of the grid. You should measure +12 VDC on the left side and 0 VDC on the right side.
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On the right side of the grid, confirm 0 Ω resistance from the grid to ground using the ohmmeter function.
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If you read 0 VDC on both sides, there may be a bad connection on the +12 VDC (left) side. If you read +12 VDC on both sides, the grid's ground connection (right side) is likely faulty.
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Check the electrical connectors on either side of the grid to confirm they are making good contact.
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If +12 VDC is not present on the left side, check for a blown fuse or a faulty defroster relay:
- Early cars (early): Defroster is powered via Fuse #4 (25A) on the Auxiliary Fuse Panel (under dash, driver's side — LHD).
- Later 944s: Defroster is powered from Fuse #13 (30A) on the Central Electric Panel (under hood).
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To test whether the relay is the cause of the problem:
a. Remove the relay from the relay panel. b. Turn the ignition switch ON. c. On the relay panel, jumper defroster relay contacts 30 and 87. Check for proper defroster operation.
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If the electrical connector tab has become detached from the rear window defroster grid, adhesive kits are available specifically for this repair. Clean the damaged lug and glass thoroughly before attempting:
- Permatex 21351, Electrically Conductive Rear Window Defogger Tab Adhesive
- Loctite 21351, Rear Window Defogger Tab Adhesive
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If the defroster grid lines are damaged, repair kits are available:
- Permatex 15067, Quick Grid Rear Window Defogger Repair Kit
- Loctite 15067, Rear Window Defogger Repair Kit