North American Turbocoupe Organization



Another Rear Window Defogger Problem
t-bird88 Offline
Senior Member
#1
I have been messing around with this damn thing for the last 5 hours and have not been able to get anything accomplished.

Here is the deal: My nephew, turbotronic, came by and complained that his rear window defogger did not work any more. I have done continuity checks on the wires and the fused links and they all checked out. I have checked and changed the fuses, still no luck. I have continuity all over the place except for one wire. The yellow wire that, I think, comes from fused link V and goes to the defogger relay only has voltage when the button is pushed and held in. And when this is done, the light on the switch still does not come on. When the button is let up, the power drops to zero.

I am getting voltage on the light blue/pink wire, but there is still nothing showing me that there is power to the switch itself. I have checked for continuity on the switch itself and even tried two other switches, and still no luck. I have taken the relay out of my car (a known working one), and still nothing. Now in the search that I did, there was a few mentions of the timer for the circuit. But in my EVTM, there is no mention of the timer in the schematics, WTF? I have looked at 10 different pages with the schematics that have to do with this and I am still at a loss with this.

The book shows, on page 114 of the EVTM, that the yellow wire should be hot at all times, and yet I am not getting any power to the relay. That is where it gets its power from correct?

The bottom line is I have swapped out head units, switches, and relays, and I am not having any luck. What am I over looking here?

Jim B :mad: .
Gunmetal Grey 88 TC!!!!
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DonH Offline
Posting Freak
#2
Yellow wire is correct as the power source. Do you have the electronic heater A/C control or manual? My book shows manual control has the timer integrated with the switch and the electronic with a solid state relay separate from the switch. With the key in run 12v on the light blue/pink wire activates the relay. Check the black wire for ground, if not a good ground the relay, timer, and light wont work. If the relay works you should have 12v on the gray/yellow wire. With the manual control the only continuity across the terminals will be between yellow and gray/yellow when the relay is on. The contacts in the switch itself are isolated from a continuity check by the timer circuit.

I have never been able to activate that switch without the engine running.
1987 TC stock except ATR 2.5"
1983 Pontiac Transam T-top 5.7 T56 [email protected] top speed: 176mph
1978 Fairmont 2.3 4-spd Big-top S/W
1946 Willys CJ2A 134.2ci L4 No-top
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t-bird88 Offline
Senior Member
#3
Well, his is just like mine and it is the electronic one. The weird part about all of this is that I get 12V on the yellow wire, and with the key on, the blue/pink wire has 12V. The thing that I don't understand is why won't the thing work any at all. The little light won't come on, after trying 3 different switches and two different relays.

I will continue to read my diagrams and see if there is something that I missed. It will be a few more days before I can work on his car again, he had to go back to work.

Jim B Big Grin .
Gunmetal Grey 88 TC!!!!
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DonH Offline
Posting Freak
#4
The only thing I can see that would stop a known good unit from working is a bad ground or a bad connector.
1987 TC stock except ATR 2.5"
1983 Pontiac Transam T-top 5.7 T56 [email protected] top speed: 176mph
1978 Fairmont 2.3 4-spd Big-top S/W
1946 Willys CJ2A 134.2ci L4 No-top
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Footintim Offline
Member
#5
Hi,
Have you tried a continuity check across the glass? I have seen a break near the main connection at the glass on either side cause this issue.
Tim
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Jeff K Offline
Administrator
#6
The light will still come on even if the defroster grid is disconnected.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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Footintim Offline
Member
#7
hummmmm
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