Bad day today...Heated rear window help needed please!
 

Try as I might I can't fix the demister on the rear window. The switch works, the relay works....but still no joy. I concluded that the bloody thing isn't connected. I removed the rear parcel shelf and side trims and I expected to see some wires and/or connectors. I couldn't see anything. Could someone please explain, describe, draw picture, send photos or something of how (and where) the rear window actually connects. The car is a '75 Targa.

Desperate Tony

Can't be much help. My PO didn't put the harness back in when the car was painted.

On a coupe. The harness is imbedded in the window seal. Not built in. But I'm told you cut out a trench for it to sit in.

There is a harness connection right behind the fuel filter. The demister harness comes right thru the car right at the left engine bonnet hinge.

Check the rear fuses, again. With the age of our cars. Those copper fuses holders have seen their share of time and elements.

Not much help.........but maybe some direction. Good Luck.

Well....
 

The thing is.... I looked under thew seal (as best I could) and can't see how any wiring is supposed to attach to the window. There are four metal things on the edge of the glass less than an inch long and shaped like a minature metal bridge. Do these have anything to do with it.. are they supposed to have wires coming off them? They are soldered to the demister element but they appear to be attached to nothing.

I'll be as much help as I can be, my defroster isn't wired up but my wires are still intact. As far as I can tell the wires have connectors on the ends and attach to those "bridges" you see. How exactly they hook up I'm not sure. A guy in the local Porsche club is going to let me look at a car he has to see how they hook up. I have the 2 stage unit so I have to black "bridging" wires and 2 grounds and 2 power wires, 6 total. The restores guide to the 911 states that a hole is punched in the rubber surround for the wires to pass through then the wires lay in the rubber seal around the glass. Several people on this board have advised me to get the defroster hooked up by a shop and not attempt it myself.
Hope this helps, by the way mine is a 78 SC.

Thid definitely helps...
 

This is good and confirms my suspicions... the window bit of my wiring is missing. i would like to hear of peoples experiences of doing this job... a diagram would be good.

Thanks very much for the help. Please could you send any info you get to tony.swede@virgin.net if it isn't too much trouble... I would greatly appreciate it.

Here is a photo of were the harness comes into the eng comp.
I couldn't get a good photo of the wiring laying in the window seal. But if you use a small plastic hook on the inside of the seal, you can see a channel where the wire should lay. Also on my 88 there was a placard with the p/n 991.612.032.04 on the harness.
There was two brown wires [grd] also coming out of the harness for the 3rd brake light.

<b<Still Struggling
OK... here goes.

I've had another look at the fuse/relay/wiring/wiring diagrams.

The diagram implies that I am looking for brown (earth) and red/white (live) wires to heat the rear window. I can see a red/white wire coming from the relay box in the engine compartment and there is a red and white wire on the multipin plug that goes to the relay box. But I can't find where they go to.


Does the wire in the multipin plug go straight to the window?

Or does the wire coming out of the side of the relay box/fuse holder go to the window?

Either way there is definitely nothing going to the window.



If I can find out which of the red/white wires is supposed to go to the window I can cut it and reconnect it straight to the window. And I assume I can get an earth from anywhere. But the thing is I still can't for the life of me figure out how and where to attach pieces of wire to the window - there is a picture in the haynes manual that is about as much use as an ashtray on a motorbike.... I think something is missing.

Please forward your considerations.

Merry Christmas
__________________
TSwede
</b>
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Tony,

Two requests, please?

1. Keep all of the data and questions in this thread and don't add anything to the other thread on this same subject ... OK? It makes it rather difficult to keep track of two threads that pop up and fade away at different times. I have copied your post frrom the other thread to this one, to get all thoughts on one track.

2. You need to determine whether you have a single-stage, or two-stage relay and switch ... does your demist switch have one or two detents or positions when you pull it out? In the Haynes manual, all of the circuit diagrams prior to the SC are shown as single-stage. But, the two-stage switch and relay, and three-panel electric grid were available as early as the 1969 911S. even though I haven't seen any factory schematic diagrams that included that option ... at least not in my USA factory manuals.

If you do find that you have the two-stage option, then the schematic diagram in Haynes on p. 304 can be used. Note that the center grid is for stage one, anthe upper and lower heating grids are activated in stage-two.

Thank You all
 

Hi All... I have enough info now to tackle the rear window. i need to get my hands on a wiring harness. The window is a two stage one... I should have mentioned - sorry. Also I can't see any kind of multipin connector on the fuse/relay box to attach it to. There is on on the back of the metal box (towards the back of the car) but it is used and the wires disappear off into the engine compartment out of sight. There are no others. It would help I suppose if i knew more people with 911's and I could copy these things - but this will come. I appreciate your healp and patience in the meantime.


Happy Chrismas to all

Best Regards

Don't take the window out unless you really, really want the rear defroster. All the wiring and figuring things out will be easy compared to getting the window back in - especially if you accidentally bend the aluminum bezel...

-Wayne

Tony,

The 'front' 14-pin connector is actually in the middle of the relay/fuse/CDI panel, right below the Voltage regulator. I call it 'front' because it goes to the front of the car, and because the 'rear' connector goes to the engine, and it is at the rearmost location.

However, on my car, which also has the two-stage relay and switch, the two power leads off the relay come off the fuse/relay/CDI panel separately in a two-wire pigtail into a three-wire connector using only two of the contacts. Mine are Red and Red/White wires directly off the relay terminals 87 and 87a ... but yours should be colour-coded Red/White and Red/Black, per the factory diagram.

re: 'Aluminium Strip'
 

Hi all... thanks for the posts again... I am off looking at the bottom of the relay to trace the contacts later... poss tomorrow. Also what is the aluminium strip referred to by Wayne @ Pelican Parts. I noticed some reference to a chrome strip in the manual but I think that referred to the coupe - mine is a Targa. lease let me know then I can be suitably put off causing myself a world of pain.

Best Regards

All,
My wires are not attached to the window, but do have connectors at the ends of the wires. The wires have a "female" spade clip on them and they look like they just slide onto the connectors on the glass. But I don't know which wires go to which conectors, anyone out there that has their connections intact, please post which color wires go to which connectors. If I can get pics of the ends of my wires I will post...

plain fan,

Since you didn't post the year of your car, or the wire colors in question, take a look at this diagram, which, except for the color code for the wires on terminals 87 and 87a, and the internal wiring error inside the pn# 911.615.115.00 relay, matches my car ...

The factory service manual error for the relay, and testing instructions for the relay can be found in the following thread:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=53318&highlight=rear+de fogger+relay

Assuming you have the two-stage circuit, pull the relay, make a set of 10-12 foot test leads for your multimeter ... and identify which wire goes to terminal 87 (circuit track 2 in the diagram) of the relay, and that one connects to the center grid. The wires connected to terminal 87a (circuit tracks 8 & 9 in the diagram) go to the upper and lower grid. The wires on the other side of the car are all brown, meaning ground, so it doesn't matter which grids they go to!

<img src="http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_defogger.jpg">

Thanks Warren, by the way it is a 78SC.

My two-stage dash switch pulls out for off/on and turns side to side for high/low. The aluminum bezel Wayne mentions is what the glass guys call a 'chrome' trim, even if it's black anodized aluminum. Wayne is warning you that a rear-window removal and reinstallation is a high price to pay for defroster repair. Apparently, window replacement is difficult.

FWIW, I am told you can re-shape a bent bezel by using the window glass as an anvil. Carefully. This ensures that the bezel has the same shape as the glass.

You might be able to just poke a wire or two down into the rubber gasket, from the inside, so it makes electrical contact. Then hide the wire as best you can, under the gasket if possible to the bottom of the window.

Perfect
 

I believe I now have enough information to do this job without removing the window. If the window ever has to come out I could do a better job then. But as it is always so damp and miserable (therefore foggy windows) around here that I feel I must do this soon. This has been a good and productive post and I am obviously not the only one with these problems. Thanks to everyone and particularly to Bob and Early S Man.

Best Regards

PS

Anyone in the UK have a demister (front) motor to sell... mine is well fried..