I haven't had a working rear defogger for months now. I've finally decided to take a look at it. I tore off the back panels, and discovered the power wire for the defogger is purple and runs down the driver's side. Of course the ground is black, and it runs along the passenger side. I checked the fuses, they were fine, the light on the switch will not come on if they're not working/connected anyways.

I pulled off the front driver's side panel today to see if I could locate the problem. I found a purple wire and got out my multimeter to test for continuity... none... but I got a power reading -12v. Hmm weird, there was no key in the ignition and a reading of negative 12v? Then I went to test the ground, I just tried grounding it to any available ground wire, same thing, -12v reading. Maybe it's grounding out?

I was never able to find any of the relays, they may be on the passenger side. I managed to dig up a wiring digram, linked below (PDF format.) Any suggestions would be greatly appreciated.

Rear defogger diagram: http://www.clickright.ca/86 Calais Defogger Circuit.pdf

Hmm I just checked at the fuse panel with the fuse out and power on, and I'm getting a 12v reading by probing the fuse contacts with my voltmeter. From what I understand I shouldn't be getting any reading unless there's a fuse in there.

Um, 12v is the b plus feed, no fuse no where to go, but the 12v is normal. 12v is on one side of course.

Um, 12v is the b plus feed, no fuse no where to go, but the 12v is normal. 12v is on one side of course.

Hmm.. any ideas how I could troubleshoot this guy? I'm good with general electronics, I'm just new to vehicle electronics.

Ok go to the glass and put a test light on the B plus side of the glass connector, if current is there then check the gd side for continuity, on the other side of the glass.

Absolutely no current going to the window. The ground with the vehicle is good, with very little resistance. Window continuity is also good.

Any ideas where the defog control is located? Maybe even the timer, though it seems to work, as the indicator light turns off after 10 mins as it should.

I didn't see it under the driver's side dash when i pulled everything out. I don't remember seeing it on the passenger side either, when i pulled that apart a few weeks back.

Did you check the connector at the glass or the wires in the glass, also the relay can close and turn the indicator lite on but not deliver current to the glass. Not sure where the relay is, may be behind the glove box.

Did you check the connector at the glass or the wires in the glass, also the relay can close and turn the indicator lite on but not deliver current to the glass. Not sure where the relay is, may be behind the glove box.

I checked both the connectors and the wires. I just rechecked them today, and discovered that when the defogger switch is activated, there is slightly increased resistance to ground. I'm thinking more and more it's the relay so I'm going to have to hunt it down.

Alright, I found the location of the relay! It's behind the glove box, located on the right hand side. I was having trouble getting it out, and it started raining on me, so I'll have to have a look at it tomorrow. Anything specific I should be looking for?

Finally got that bugger out, man that was a pain. Here's what I found:

The relay appears to be working normally, upon switching the circuit on, the relay clicks, and +12v goes out the D connector (PPL/WHT) I took my multimeter and plugged the negative side into that connector and took the positive side and touched some wires on the window. All had a -12v reading. Any ideas?

If you have 12v to the wires and there are no breaks and the glass does not get warm, the ground from the glass to the body is bad.

If you have 12v to the wires and there are no breaks and the glass does not get warm, the ground from the glass to the body is bad.


Hmm.. Ground was fine though, tested from battery ground to window. Hmmm Any other ideas?

After some thinking it has occurred to me that it could be the circuits going to the + side of the window that have good ground, not the ground for the window itself, would that make sense?

If I disconnected the relay, I think should be able to rule that one out. I'd love to just replace the ground wire anyways, but I can't tell at all where it's going.

That what I meant

Well I removed the relay from the circuit and tested the window for ground and it was good. I'm really lost now :banghead:

Either you are doing something wrong here or I am misunderstanding what you are saying, get the voltmeter on a window line on the b plus side of the defogger glass, then get the gd side of the voltmenter on to the ground connector for the glass and see whats what. Make sure there are no breaks in lines also. If you have 12v at the glass lines and a good gd at the other end of the glass, then either the purple wire has high resistance somewhere so the amps don't reach the glass or your lines are bad in the glass. What is the connection with removing the relay and checking the glass ground?

Either you are doing something wrong here or I am misunderstanding what you are saying, get the voltmeter on a window line on the b plus side of the defogger glass, then get the gd side of the voltmenter on to the ground connector for the glass and see whats what. Make sure there are no breaks in lines also. If you have 12v at the glass lines and a good gd at the other end of the glass, then either the purple wire has high resistance somewhere so the amps don't reach the glass or your lines are bad in the glass. What is the connection with removing the relay and checking the glass ground?

I'm sorry, but when you say B plus side, I really don't know what you're talking about. Anyways, the only time i have ever been able to get a voltage reading from the glass was by connecting my dmm to the PPL/WHT wire that eventually supplies power to the PPL wire at the window. (so PPL/WHT to PPL connector on window) Other than that, there's never been any voltage present. (either by testing for voltage via the connectors on the window or by grounding to the chassis and testing for power at the PPL wire connector on the window.) I figure there must be a break in the PPL wire. Any idea what the "C200K (WHT)" thing is where the PPL/WHT wire changes to PPL?

As for removing the relay, that was just so that I could isolate the ground for the window, so I knew it was actually the window that was grounding, not the connections at the relay.

The gd for the window is independent from the relay and just grounds the glass, if you have 12 on the ppl wire from the relay and it disappears before it gets to the glass, run a seperate wire from the relay just for test purposes and see if the glass works. Are you famliar with checking dcv circuits in a car, if not you better read up on it or you will get lost here, even though this is a very basic circuit.

The gd for the window is independent from the relay and just grounds the glass, if you have 12 on the ppl wire from the relay and it disappears before it gets to the glass, run a seperate wire from the relay just for test purposes and see if the glass works. Are you famliar with checking dcv circuits in a car, if not you better read up on it or you will get lost here, even though this is a very basic circuit.

Yeah I was actually just out looking at it, and was thinking i should do that. I bypassed the relay when i went out, ORN/BLK to PPL/WHT and no cigar. I'll have to pull off all the plastic trim from that side just to get at it, so I'll have to do it on a nicer day. I'm fairly familiar with basic circuits, so hopefully I can get by.