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FWIW I have taken apart a few hatch trims and found the defrost wires have been driven into the attach clips they have small spikes on them
the side trim tap off towards the center of the car
I think you better check at connectors T3 & T4, they are inside the car, no need to take off the mirrors, yet… …
Worth a quick check: I took a look at the wiring diagram and didn't see those connectors, any idea where they are (probably similar to an 89 but at least it gives me a rough idea where to look.
Also Mr. Merlin, is there a specific trim piece to remove on the rear to check those connector clips? It's cold but sunny today so I could do a bit of hunting...
You can find them on page 97-239, region E14 and G14.
They are nameless on that diagram ?!?
Attached part start in lower right corner, Relay I-II, 87 then E22 then pin 9 of the connector to pin 3 of the mirror.
You should find them close to the doors, the driver one above to the shelf, the passenger one above LH & EZK units.
Good luck… …
Unplugged the driver's side harness plug (it's big, easy to spot), put in a 20a fuse (underfuse a bit for testing) turn on car, turn on defroster.
No blown fuse. I can see the voltmeter drop and the light is on in the switch, so looks good even when pressed.
Plug in driver's side door, fuse blows.
So it's in the driver's side mirror. Pulled the mirror off and I can see the wire insulation is slightly cracked. Possible it was making contact with the mirror frame, which would be a ground. Will try insulating it again with some shrink wrap....
Well that didn't work. Still blows fuses. I checked the mirror, it's 15 ohms but the resistance between the wires at the mirror is zero with it unplugged from the car at the harness.
Which means the short is inside the door. Which means I have to pull off the door panel.
Again.... I am *really* getting good at pulling door panels, but I was meaning to fix some of the plastic plugs and put new vapor barrier anyway in the spring. So eh....
In the meantime I removed the gray pin from the harness so I could plug in the rest of the door. All other defrosters are probably working, will find out with the next snow/fog.
Thank you Stan, appreciated. There's something else interesting: The wires that go to the mirror heater itself are pretty thick, however the wires at the harness plug that power the mirror defroster are quite small. As in 16-18 gauge size wires. I'm wondering if Porsche figured there would not be that much current drawn by each wing mirror, and if we do the math it's
12 ohm mirror, 12 volt battery, i=E/R or i=12/12=1 amp. Which is not a lot of course, and well within the limits of 18 gauge wire. With P=I*E, we are looking at a max heating amount of 12 watts, or probably 6 watts on low setting.
However if the mirror shorts, it's possible under max defrost that the mirror wires could get the full 25 amps as they are in parallel and short directly to ground. That would require a 10 gauge wire to not melt, so I'm now wondering if the mirror shorted out, the wires in the door melted, shorted, blew the fuse, and the guy tried to pull the mirror, broke it, stuck a cheap silver reflector on it, and sold it to me, I replaced the mirror properly, and the car's defrost has been wonky ever since due to a burned out pair of wires in the door.
Not familiar with AWG wire size's, more mm²
But you are right, sometimes it's strange?!?
According to the drawings, from CE panel to the connector it's (only) 0.5mm², then from the connector to the mirror resistance it's 0.75mm².
For sure way tooooooooooooo small in case of short circuit, but since that happens in a blink of an aya, I wouldn't bother about that.
At least you found the problem, good luck solving it... ... ...
Good news: Last night we had some snow so I fired up the engine and hit and turned the defroster button for max power. Sure enough the rear window started to clear on the top and bottom elements, and the snow on the passenger mirror started to melt. This is progress!
Still haven't had the time to pull the door skin and check the harness. Been working 100% on fixing the passenger door issues, will do this once that's done (and parts get here. Someday.)
02-10-2019, 06:50 AM
