Rear window defog circuitry. - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 12-13-2005, 09:46 PM   #1
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Default Rear window defog circuitry.

I did a search for this, but nothing came up for the 1992-99.

My 1999 LeSabre has a malfunctioning rear window defog.
The switch works fine, but the grid does not heat up.
In my Haynes manual, there is nothing in the diagrams about it. The wires in the back are still connected to the grid.
I can hear the relay kick on when I hit the defog button, all the fuses are OK (altho i have not looked at the hidden fuses beside the glove compartment)

I would like to know exactly where this relay is, so i can test it completely instead of just listening for it.

Does anyone know exactly where the wires run from or of any common problems?
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Old 12-13-2005, 10:14 PM   #2
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One of the strips on the window might have gotten cut. Not sure if this would knock just one or all of them out, but I have heard this is sometimes the cause.
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Old 12-13-2005, 10:26 PM   #3
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Quote:
One of the strips on the window might have gotten cut. Not sure if this would knock just one or all of them out, but I have heard this is sometimes the cause.
three of them got cut in my 95
http://www.bonnevilleclub.com/forum/...hlight=scraper

it still worked except for a small circle in that area...
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Old 12-13-2005, 10:40 PM   #4
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This one sounds like the whole thing.

Keep in mind that a 'clicking' relay is not a good relay. Just fixed driverjohn'* ELC for the first time in probably 10 years. It was a relay that was clicking away just fine.

Your relay is PROBABLY above the passenger footwell. Remove the hushpanel, and toggle that switch until you 'feel' it. I suggest replacing it as a troubleshooting step. They're cheap.
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Old 12-13-2005, 10:59 PM   #5
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I do know that with the relay clicking does not mean it is making continuity,
BTW all the grid lines are in good shape.

If just one or a few got cut, it would not knock out the whole grid cause the lines are in parallel connection.
I will check it out more and post my findings.
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Old 12-14-2005, 01:14 AM   #6
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Rear defogger relay should be in the passenger side relay center (behind the hush panel)...position G.

Wires:

purple: rear defogger element feed
white: rear defogger relay output
orange: Fuse output - battery
brown: fuse output - ignition

There is a trouble shooting/diagnosis section for the defogger as well that I will need to research.
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Old 12-15-2005, 10:46 AM   #7
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Thanks to Echo for the wiring tips.
After much digging around in the lower passenger side of the dash, I dug out the relay, it was working perfect, did the coil test and the contacts were working as well, par multimeter resistance test. 0 to infinity with the coil activated/deactivated.

I pulled off the rear internal trim panels in the back to discover a burn out module.
It connects the defog grid as well as the two grids that act as the stereo antenna.
On my lesabre, this module was on the rear passenger side.

I do wonder what the hell caused it to burn up like this. I also wonder if any H-body 92-99 module would work so long as the model has the rear window grid type antenna.

I REALLY do not want to buy one of these from GM, as we know dealer parts cost a fortune.
was trying to stick a photo if it in here, but it is not wanting to take.
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Old 12-15-2005, 11:19 AM   #8
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Good find. I was going to send you to the back grid next....I noticed there was that module there. FSMs don't indicate whether a part is ineterchangeable, but I would suspect that one from another h-body would work. See if you can find a part number and maybe we can determine what other cars used it.
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Old 12-15-2005, 11:27 AM   #9
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Impatient...

Since you have the bad part in hand. Take the part number off it. Go to www.gmpartsdirect.com and plug in that part number. See what other vehicles come up as a cross reference. I should be going to the junkyard this weekend..probably and can pick on up for you if there are any donors available.
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Old 12-15-2005, 11:44 AM   #10
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It is # 25623688

I would like to see how to do this cross reference for applications.
Like i said, this one is for grid antenna and the defog. Not all H'* have both features, i don't think.

I did come across that site, and i am maybe going to go to the junkyard here soon.
Would be nice to have a list of vehicles to choose from.
I just hope they are ALL burned out, you know how in some cars, EVERY one throws the same part?
I am still suprised that my thread is the only one like this in the 92-99, and limited threads returned from the search.
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