Where do rear window defrost wires unplug?

[aigel]

exc911ence:

The fuse is 'fed' from underneath. It really is time for you to crank out the voltmeter and start measuring the resistance of the window and measure if there is voltage on the incoming side!

George

[RoninLB]

aigel's in charge

[RoninLB]

the 7 "S" numbers are from left to right

18, 19, 20, 21 ... "to battery"

12 ... "to ignition/starter switch"

24, 23 ... "to generator"

[86 911 Targa]

Originally Posted by aigel

k9handler:

That only would work if your problem is in the supply of the juice, not in the wiring of the window!

I am learning myself here, but I think it is +12 V to both of the connector's contacts. I guess the heating relay box might alternate the juice between those two cirquits or do something else to spread the joy...

I'd recommend measuring resistance on both connector pins against ground and see if it is the same. If one is considerably higher or zilch, the problem is upstream from the supply and switching won't help you.

Since the top and bottom are a unit, I'd think something in the wiring / window is fishy if only the top works, w/o the bottom.

This all said, I hope someone can confirm that draft of a wiring diagram that I threw up here! It all depends if that's correct, but if you read my thinking out loud above in the edited comment, it seems to all make good sense.

George

After a somewhat intensive diagnostic to fault isolate our rear window defogger anomolies, I finally contacted the Hella folks for a definitive answer as to why the upper and lower elements on our '86 Targa never activate.

I did confirm that relay #2 on the PC board never closes precluding any voltage on contact 87a to the upper and lower elements.





It is my understanding that the 993's have a 15 minute time out rear window defogger ckt designed into the rear window defogger relay.

Here is the response from Hella which, with due respect to Porsche, I find to be a very unusual approach.

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Hi Gerry,

I did get an answer form the engineer. I attached a printscreen of his email.

He is saying that the defogger has a certain switch-on and switch-off behavior. The first stage of the heating is working with 10.5V, the second stage of the heating is working with 12.8V. That means this second stage works with a new battery or the engine is running.

He also mentioned that there are no time delays in the relay integrated. If the second stage is working it will switch of below 11.0V automatically.

Maybe you would like to try these different voltages with the relay.

I hope this will help!

Thanks
Josef