Where is the front windshield defogger relay in an '83 SC?

[tirwin]

Folks,

I have been tracing out a parasitic battery drain. I finally traced it out to a red wire on the bottom of fuse 17, but I had no idea what it went to. None of my normal sources had a red wire on the bottom of fuse 17 (well, one did but it was actually incorrect).

I finally discovered the answer in the 'Defroster addition' diagram here:
Pelican Parts - Porsche 911 Parts Listings & Diagrams

There is a red wire that goes to pin 30 on the Windshield Defogger Relay. Well, I don't have the front windshield with the defogger built in.

I'm guessing that the factory harness includes this wire (even if it's not used) and it's somewhere in the car but I don't have a clue where to look for it. I could tag it and tape it off, but I'd like to at least trace it out to make sure there isn't some other lurking problem. I suppose the relay would not be present but I don't know where to find it. I suppose it would be somewhere behind the instrument panel or fresh air blower?

Anyone have any ideas where to look? I've circled what I'm talking about in this picture.



PS - the wiring diagram from colorwiringdiagrams.com is nice but it contains too many errors to trust except for the most basic things.

[Neilnaz]

I don't know whether this helps but in my 1971 the defogger relay sits on the metalwork in the engine compartment close to the CDI and the 3 way fuse holder.

Cheers, Neil

[Neilnaz]

Ahhh, just realised you are looking at the front - my bad

[86 911 Targa]

Originally Posted by tirwin

Folks,

I have been tracing out a parasitic battery drain. I finally traced it out to a red wire on the bottom of fuse 17, but I had no idea what it went to. None of my normal sources had a red wire on the bottom of fuse 17 (well, one did but it was actually incorrect).

I finally discovered in the answer in the 'Defroster addition' diagram here:
Pelican Parts - Porsche 911 Parts Listings & Diagrams

There is a red wire that goes to pin 30 on the Windshield Defogger Relay. Well, I don't have the front windshield with the defogger built in.

I'm guessing that the factory harness includes this wire and it's somewhere in the car but I don't have a clue where to look for it. I could tag it and tape it off, but I'd like to at least trace it out.

Anyone have any ideas where to look? I've circled what I'm talking about in this picture.



PS - the wiring diagram from colorwiringdiagrams.com is nice but it contains too many errors to trust except for the most basic things.

https://www.google.com/search?q=porsche+front+window+defogger+relay&rlz=1T4GUEA_enUS570US570&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwic8ZDwhLLKAhVKwGMKHYMIDdYQsAQIPQ&biw=1347&bih=839&dpr=0.95
^^^^^
Hope this helps.

Good luck,

Gerry

[tirwin]

Originally Posted by 86 911 Targa

https://www.google.com/search?q=porsche+front+window+defogger+relay&rlz=1T4GUEA_enUS570US570&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwic8ZDwhLLKAhVKwGMKHYMIDdYQsAQIPQ&biw=1347&bih=839&dpr=0.95
^^^^^
Hope this helps.

Good luck,

Gerry

Thanks but I don't see what I'm looking for. I'm trying to figure out where the wire would've gone from the fuse panel. I'm not sure where the front defogger relay would've been located in the car.

[gomezoneill]

Strange I've never heard of or saw a front windshield defogger on a 911.

[timmy2]

Did a little checking for you.

The single connector terminal for the Black wire to the defroster is marked T1d.

When checking terminal locations in the factory manual, it indicates that connector is behind the fuse box. Red wire to a black wire!

Thus, I would conclude the relay is mounted in the front fuse panel. Though the ground Brown wire is shared with the lighter ground wire, so it could be back behind it! Porsche liked to run wires everywhere!....

Have you identified and labeled all your fuse panel relays? Is there one without a relay mounted?

Is this photo of the factory manual page any clearer?

[tirwin]

Originally Posted by gomezoneill

Strange I've never heard of or saw a front windshield defogger on a 911.

They are rare but they do exist. If you have a rear window defogger, you pull the knob straight out to turn it on. Try turning the knob and you'll find that it will turn 90º. That would turn on the front defogger if the car was equipped.

The front windshield is different in a car with this option. If you see one, you will notice there are very fine wavy lines in the glass. The lines are the heating element. These windshields are about 5-10X the cost of a regular windshield.

[tirwin]

Originally Posted by timmy2

Did a little checking for you.

The single connector terminal for the Black wire to the defroster is marked T1d.

When checking terminal locations in the factory manual, it indicates that connector is behind the fuse box.

Thus, I would conclude the relay is mounted in the front fuse panel.

Have you identified and labeled all your fuse panel relays? Is there one without a relay mounted?

Is this photo of the factory manual page any clearer?

I was hoping you would chime in.

All of the relays in the front fuse panel have been accounted for and there is no relay there (in the front) that has an open plug. There is a space that a round relay could go in the 6th position in the panel (next to the fuel pump relay) but there is nothing there. Page 971-4 in the Bentley says position 6 is not used.

Table d. on pages 971-6 to 971-8 of the Bentley makes no mention of the front window defogger relay at all, but it clearly shows items related to the rear window on 971-8. Another Bentley omission I guess.

Just for giggles I disconnected all of the black relays yesterday and the draw still existed before I disconnected the red wire on the bottom of fuse #17.

I guess the next thing is to trace out where the wire goes but it is hard to do that without messing with the wire bundles. Or I just tape it off with a label and call it a day.

[Pazuzu]

Hey Tim, did you ever find this out?

I too am going through wiring, and I too have a red wire coming from the bottom of fuse 17, and I too do not have a front windshield defogger.

I assume that the red wire goes into a relay base somewhere with no relay in it, and then a blank or taped off wire going out (the red wire into the 1-pin terminal that timmy2 talked about).

I'd love to remove this system if you ever actually found the relay/relay base. Otherwise, it looks like you can just remove the red wire from the fuse panel, and fold it away somewhere, since it was the power (30) wire for that relay.