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Skip

Rear / Windshield Defroster Switch

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Hi again,

OK, so I've been working on the wiring to determine continuity for my defroster (car is 1984 911 ROW) which has both rear and windshield defroster I replaced the switch as it had a burn smell on it with the appropriate OEM switch. My question is this: the Bentley manual does not show a windshield defroster at all, and the only one I can find similar is the Pelican post for an 82SC. That said, the SC diagram shows only a 1,0 diameter Bk (black I believe) wire at point "III" and I have two different options: (1) single black wire or (2) a multiple connector with 2 x black and 1 x red/white wire. I believe it should be the single wire, but the strange thing is that no diagram shows a mixed red/white with 2 x black on it. The only remaining location for this connector would be point "15" which shows either 2 x 1,5 diameter black on the 82SC diagram or a single black in the Bentley Manual.

The Bentley manual also has no connection at point "III", so I expect this is the front windshield connection.

Final question relates to the orientation of the switch itself. It seems to have three different settings which I can't understand:

(1) turn clockwise

(2) pull on

(3) pull on and turn clockwise

Can anyone confirm what each should do?

Thanks and Merry Christmas.

Skip

Edited by Skip

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Hi again,

OK, so I've been working on the wiring to determine continuity for my defroster (car is 1984 911 ROW) which has both rear and windshield defroster I replaced the switch as it had a burn smell on it with the appropriate OEM switch. My question is this: the Bentley manual does not show a windshield defroster at all, and the only one I can find similar is the Pelican post for an 82SC. That said, the SC diagram shows only a 1,0 diameter Bk (black I believe) wire at point "III" and I have two different options: (1) single black wire or (2) a multiple connector with 2 x black and 1 x red/white wire. I believe it should be the single wire, but the strange thing is that no diagram shows a mixed red/white with 2 x black on it. The only remaining location for this connector would be point "15" which shows either 2 x 1,5 diameter black on the 82SC diagram or a single black in the Bentley Manual.

The Bentley manual also has no connection at point "III", so I expect this is the front windshield connection.

Final question relates to the orientation of the switch itself. It seems to have three different settings which I can't understand:

(1) turn clockwise

(2) pull on

(3) pull on and turn clockwise

Can anyone confirm what each should do?

Thanks and Merry Christmas.

Skip[

Sorry,

I received your Email, but I'm not at all familiar with any front window defogger circuits.

Try this:

http://www.cannell.co.uk/Manuals.htm

Good luck,

Gerry

  • Upvote 1

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Thanks to both of you. I'll look through each piece and give it a whirl in the morning. Will post results.

Skip

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So, this morning I crawled under the hood, removing the requisite fresh air plenum and blower. Easy enough to reach the back of the switch to flip the two wires around. Voila, switch lights up in all three positions. Now all I need to do is fog up the windows to test it out. I used both diagrams as well as downloaded the older manual 73-75 from Cannel UK which had a great additional diagram showing a front windshield defroster. Although the switch is slightly different and colour codes vary, the concept seems the same. The two diagrams from Loren, enabled the colour coding. Seems like the windshield relay is behind the front fuse box - not sure I want to remove that unless I have to - sooo, will go and try to create some humidity to clear. Thanks again to both.

Edited by Skip

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Well, I'm now back to establishing my problem with the rear window defroster. I have conducted several tests (incl testing the defroster relay at the rear, and all seems ok - at least to the to pin connector after the relay with red/wh and red/blk wires which appear to go to the rear window. I also believe that the two ben ground wires come in and attach directly behind the fuel filter on the left side of the engine compartment). I believe this ground position is identified as G406, but the Bentley manual does not identify the connection point for the rear window ground wires specifically that I can find.

The testing completed is as follows:

(1) From the Pelican Site I(Early_S_Man) found the follow test (which all worked as expected):

a. Connect pin 31 to ground;

b. Connect pin 30 to +12 Volts;

c. Connect 86 to +12 Volts - you should hear an audible click inside the relay (which I did);

d. Measure voltage at pin 87 with respect to ground... +12 Volts SHOULD BE PRESENT (which it was);

e. Connect pin 86a to +12 Volts - you should hear a second audible click (which I did);

f. Measure Voltage at pin 87a... +12 Volts SHOULD BE PRESENT (which it was);

g. Disconnect the ground from pin 31;

h. Disconnect + 12 Volts from pins 30, 86 and 86a

(2) all relay tests above were successful;

(3) I then tested the 6 pin wiring harness (which connects to the relay) and noted the following:

a. with ignition switch off - no power at any point

b. with switch in ACC or ON, power at pin 30 only;

c. with defroster switch rotated right (either with or without pulling it out) - power at pin 86a;

d. with defroster switch in any position (including rotation) - power at pin 86

(4) after reinserting the relay, I tested the power at the two pin connector and noted a parallel power of +12 Volts at red/blk connection (off pin 87a) only with a right rotation of the switch and +12 Volts at connection (off pin 87) at any switch position

(5) I then tried testing the other end of the two pin connector for resistance between the red/wh and red/blk points to ground (G406) but got nothing - am not sure if this was really a valid test however as there are resistance circuits in the diagram (not sure if I did this test wrong?)

(6) am now at the point of trying to test each line in the rear window, but wondering also, what the best methodology is to do this?

(7) Two additional things, I tested the rear window defogger base (on the driver side) with switch in on position and a test light - the light came on for a short period of time and then stayed off (not sure why, less perhaps that the relay shut down once load (high resistance) was applied?

(8) I also tested the passenger side base to ground and it appears to have connectivity.

Thanks.

Edited by Skip

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Post deleted.

Edited by 86targa

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