Rear window defog debugging

[GrimJack]

Ok, I'm at a bit of a loss here, folks. My rear window defog doesn't work, and I can't figure out a logical reason why. Here's what I know so far:

- The defog in the mirrors works, and it pulls off the same circuit according to the TEWD. That rules out the defog circuit breaker and relay, from what I understand.

- With everything connected, there is no power at the actual window terminals when the switch is on.

- If I unplug the window terminals and check, there *IS* power on the positive side. As soon as I connect the ground, however, no power.

- The TEWD makes reference to a 'choke coil', and according to the diagrams I found, it should be located in the rear hatch. However, both of my cars do not appear to have this, unless it's magically hidden inside the antenna box or something.

references:
http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=84

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=25

 

[Kai]

Ask Stuey about this one i think (supradupra) he's the guru of all things electrical...

 

[IJ.]

Check it with the Hatch closed Dave

 

[Poodles]

http://en.wikipedia.org/wiki/Choke_(electronics)

Dunno if that will help, but I've had the same issue with my defroster since I bought my car, I gave up after a while since I know the circuit on the window is pretty bad anyway from the crap tint job...

 

[bombinuass]

hmmmm i had a problem with mine only 2 strips defogged and they wernt the ones i needed to see out of. lol but i found a break in the strip and i just put clear electrical grease over it and they all work now lol good luck with your problem.

 

[supraman7mgte]

Yeah,maybe a break in the circuit might be the problem.

 

[GrimJack]

Check it with the Hatch closed Dave

Just tried that... same symptoms, though.

http://en.wikipedia.org/wiki/Choke_(electronics)

Dunno if that will help, but I've had the same issue with my defroster since I bought my car, I gave up after a while since I know the circuit on the window is pretty bad anyway from the crap tint job...

Looks like that's there to isolate the signal coming in through the antenna built into the glass from the power to the defogger... maybe to get rid of interference? Still can't find the damn thing...

Yeah,maybe a break in the circuit might be the problem.

I don't think so, seems like that would have different symptoms.

The thing that's really odd is the vanishing power... it's like some component is detecting something wrong, and cutting the power. As far as I can tell from looking at the wiring diagrams, there isn't any such functionality.

 

[IJ.]

Do you have power in the thick black wire under the doorsill plate?

The switch has a built in timer, it may have failed.

 

[jetjock]

^ If that were true the mirrors wouldn't be working

Choke is at connector C19. It's up under the rear hatch panel:

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=25

The reason voltage drops when the load is connected is simply because, well, it's being dropped across something. This is an example of why measuring open circuit voltage is bad technique. Anyway, better track it down before it reveals itself in a bad way...

 

[IJ.]

Ahhh ok never had a car here with mirror heaters didn't realise they were on the same circuit and switched by the same switch.

Only mentioned the hatch open thing as I noticed now and again mine won't draw current with it open so I'm assuming Toyota are using the striker as the ground path and that the hinges aren't adequate. (PDM displays current draw and this drops when the hatch is up but the circuit is still hot)

 

[NashMan]

you most likely have a break in your hatch glass its very common or the clip it's self

some times the easy stuff is the culprit

 

[jetjock]

Ian: Ground path is through the choke.

Nashman: You can't be serious. Better not quit your day job, whatever that is.

Dave: PM me if you need more help. This is simple stuff...

 

[IJ.]

Gary: 86.5 here "404 choke not found"

 

[jetjock]

Figures. More weird Aussie stuff. Probably the same for Canucks. We'll just blame it on Her Majesty

 

[IJ.]

LMAO we're NOTHING like those Canadians...... hang on we are a little... welll maybe more than a little... damn I have family there so guilty as charged

 

[GrimJack]

Looks like it may be another case of differences between various countries, I guess. Here's a couple pictures of the underside of a Canadian hatch - this isn't the car with the problem, it's my other '89, and it works fine. Both cars appear to be exactly the same in the way of wiring.

 

[bombinuass]

do all supras have heated mirrors? IDK IF MINE DOES.

---------- Post added at 02:22 PM ---------- Previous post was at 02:20 PM ----------

looks like it may be another case of differences between various countries, i guess. Here's a couple pictures of the underside of a canadian hatch - this isn't the car with the problem, it's my other '89, and it works fine. Both cars appear to be exactly the same in the way of wiring.

my 87 looks identical to that too. ^^

 

[GrimJack]

No, the heated mirrors are not universal. Nor were the headlight washers, or seat heaters. It is not at all difficult to figure out whether you have them... turn on your rear window defogger, wait a minute, and touch the mirror glass. If it's hot, you have 'em.

 

[bombinuass]

well i have headlight washers and rear defrost . so would my mirrors be heated?

 

[Dirgle]

While I do have a connector C19 on my 87......

... as you can see there is no coke at that location. The ground wire comes directly from the defrost grid and is soldered to the little metal frame. No capacitor and no inductors.