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Discussion Starter #1
Hello Team,

I have a 2006 Commander base 4.7L. My rear defroster doesn't work. Initially, I noticed one of the tabs had separated from the defroster grid on the rear windshield. It was flapping in the breeze. I picked up some conductive adhesive (advertised for exactly this type of repair) and glued it back to the grid on the windshield. Rear defroster still didn't work. I checked the relays under the hood in the integrated power module. The rear defogger relay (as indicated by the key on the underside of the IPM lid - it's the fourth or middle 12V Tyco relay in the row of seven) was missing - huh. I got a relay, inserted it, and tried again. Nothing.

When I depress the rear defroster button, I hear a "click" behind the gauge cluster in the dash. But there is no click at the IPM under the hood. To see if it was the new relay I inserted, I also tried a relay that was working in another position. I listened to the number 1 relay (front wipers) as my six-year-old turned on the wipers - I heard the "click," and the wipers worked. I took out that relay, inserted it into position 4 for the rear defroster, and had her press the button for the rear defroster. No click at the IPM.

Any thoughts? Thanks!
 

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The "Junction Block" is an assembly on the firewall inside the drivers side to the left of the steering wheel - it has a set of fuses on it and had a ton of circuits and relays that go through it. It also has a relay for the rear defogger.
See Junction Block explained
 

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Here is the rear window defogger from the service manual.
 

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Discussion Starter #4
This is great, thank you very much! I'll have some time this weekend to attempt a diagnosis/repair. I'll let you know how it goes.
 

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Discussion Starter #5
Update: I replaced the junction box relay, and now my voltmeter shows that there is power to the rear defroster! Looking forward to a cold/rainy day to turn her on. Thank you again!
 

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It is really called the "Junction Block"
You're welcome by the way
 

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Discussion Starter #7
Ha, sorry about that...junction block. But, bad news - the defroster grid itself is still not warming up. I confirmed there is definitely power to the two tabs that attach to the rear windshield. But no defrosting is happening...

Two things I can think of that could maybe have contributed to this situation?

1) When I first tried to re-attach the tab that came loose, I attempted to solder it. Which didn't work (I probably didn't do it correctly...). But anyway, I "prepped" the surface of the defrosting grid (it's wider around the edges) by scratching with a wire brush. Bad idea?

2) There is a small, 1/4" break in the grid in the middle of the windshield. Dunno how it happened, but it looks like it got rubbed off by something (the material is smeared on the windshield in an arc, as if something dragged it across the windshield). Could that be preventing the circuit from being completed?

Thanks and hope you're having a good weekend!
 

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Ha, sorry about that...junction block. But, bad news - the defroster grid itself is still not warming up. I confirmed there is definitely power to the two tabs that attach to the rear windshield. But no defrosting is happening...

Two things I can think of that could maybe have contributed to this situation?

1) When I first tried to re-attach the tab that came loose, I attempted to solder it. Which didn't work (I probably didn't do it correctly...). But anyway, I "prepped" the surface of the defrosting grid (it's wider around the edges) by scratching with a wire brush. Bad idea?

2) There is a small, 1/4" break in the grid in the middle of the windshield. Dunno how it happened, but it looks like it got rubbed off by something (the material is smeared on the windshield in an arc, as if something dragged it across the windshield). Could that be preventing the circuit from being completed?

Thanks and hope you're having a good weekend!
Yes, #1 was a bad idea. And #2 is most likely your problem.

.
 

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Discussion Starter #10
Ok. Also, I actually found that exact video on YouTube, so I'm going to try that today. Thanks!
 

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