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-   -   Electrical (melted wire) need diagram (http://forums.pelicanparts.com/porsche-911-technical-forum/245597-electrical-melted-wire-need-diagram.html)

steviee7 10-11-2005 08:50 PM

Electrical (melted wire) need diagram
 
Well my worst nightmare. I pull up to the store, get out of the car and push my alarm to lock the door. Door locks but no beep from the horn. Hmmm I said. Tried to unlock/disarm and nothing happens. I have to unlock door with key and then open trunk to disconnect the fuse for the alarm. At least I can still lock my car and drive home. (starter disable is not an issue without alarm fuse)
So the next day I put the fuse back in the alarm and keep trying to arm/disarm. Nothing. I fish around with my hand in the trunk area on the driver side (where a lot of wires live) After a while of poking,... Beep! And then nothing. Aha I've gotten closer to the culprit. Then (to my shock) I see a 7 wire connector with a melted wire. On one side of the connector the light grey was melted to a brown wire. And on the other side the light grey (I'm guessing since there is no insulation left!) was stuck to a white wire.
Can anyone tell me what these wires do and go. I'd like to run a new grey wire altogether. (if possible) I don't know if the elecrical diagrams on the pelican parts site are of my car. I'd probably buy a book but which one is the best (for the money)

http://forums.pelicanparts.com/uploa...1129092463.jpg

Steve

Jim Sims 10-11-2005 10:17 PM

Do you have heated mirrors? It appears the melted "gray" (probably was gray and green) wire provided power to the heating element in the driver's side mirror. It is interesting that the fault may have taken out the alarm and the central locking unit. How do fuses 8, 9 and 10 (counting from the left) look? Fuse 10 is likely the alarm fuse to orient you to the numbering system.

steviee7 10-13-2005 09:09 PM

Sorry it's been a while for a reply on my part...computer issues.

Anyways, I'll have to look at the fuses. The car had a factory alarm and an aftermarket viper alarm. So I think the fuses looked OK last time I checked. I mean they looked un-blown.

As for heated mirrors I'm not sure if I have them or not. I do think that my rear window defogger is not functioning. One crazy thing that happend the night of that crazy alarm I drove off with only one headlight. I took the headlamp assembly apart and found a loose connection and the light came back, but it seemed to fade in. I ended up replacing both bulbs and it seems fine now. (could the headlamps, if they are going bad do some thing to the electrical system?)


I've had issues in the past where my headlights would fade in and out faster with engine rpm. If I turned my rear defrost on the lights would be fine. It could be unrelated but I figure I'd tell ya.

For the grey melted wire, where does it go. Can anyone recommend a good book?

Thanks,
Steve

steviee7 10-14-2005 08:30 AM

I'm guessing that maybe my alarm, headlights, horn and central locks are fine, it's the defroster system that might have a short causing high current. I would think that I would blow a fuse before anything got too hot.
(I guess not a lot of people like to help when it comes to electrical.)

Does anyone have the Bently Publishing 911 Carerra manual? and does it have a very good electrical section? Should I buy a copy or sell the car.) by the way Amazo n.com has it for 75 bucks new.

hmmm.

Jim Sims 10-14-2005 09:06 AM

The grey/green wire "goes" (the direction the current is flowing or voltage is dropping), as stated above, to the heating element in the driver's side rear view mirror. Reading through your posts it "appears" you checked the fuses and they are okay. This circuit indeed includes the rear window defroster system and is fed from 25 amp fuse "9" (counting from the left). Does fuse "9" look like it's been heated by the passage of a high current? The short is likely "downstream" (toward the door) of the seven-pole connector shown in the above image. The wiring harness to the driver's side mirror next passes through a six-pole connector and then to the mirror. I would first look for a short where the wires pass from the body to the door. I would look there for wire damage and a short to ground (the body) or within the wire bundle.

Why didn't the fuse blow? My conjecture is that there are too many items being fed by this 25 amp fuse and the 0.5 mm (.020") diameter wire (the grey/green one) had less current capability than it's feeding fuse. So when it shorted, it melted long before the 25 amp fuse reached it's "melting" (blowing) current. This isn't the first time Porsche has done this. I suspect this is the same basic wiring system laid out for the 911's in the 60's and it has been pushed beyond the limit of good design practice with all the additional electrical accessories like heated mirrors, etc.

I'm reading from a set of 1986 wiring diagrams (21 pages!) from the OEM shop manual for Carrera's (current cost $1000 to $1200 for the set). I don't have a Bentley manual for the Carrera so I am unable to comment on the adequacy of the wiring diagrams it contains. Perhaps someone else can comment. Cheers, Jim

steviee7 10-14-2005 10:02 AM

Thank you so much Jim, I will look at the area where the wires pass thru the door and maybe inside the door to see if futher meltdown is seen.

Steve

(I had an issuse once with my VW where the car wouldn't even shut off! I found a melted wire fused to another one) yikes!!!

Again Thanks.


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