911 Targa, changing rear defogger from two-way to single?

[jsoderbe]

Hi,

I'm replacing my old Targa rear window (with an antenna hole) for a nice newer rear window from a 1986 Carrera. But, that window has more wires to the rear defogger, and I'm guessing it has a two-way (or do you say two-stage?) defogger.

So, my question is how I can connect my old wires (just two) to the new window with four wires? Anyone that has done this already?


Regards,

Johan

[86 911 Targa]

Originally Posted by jsoderbe

Hi,

I'm replacing my old Targa rear window (with an antenna hole) for a nice newer rear window from a 1986 Carrera. But, that window has more wires to the rear defogger, and I'm guessing it has a two-way (or do you say two-stage?) defogger.

So, my question is how I can connect my old wires (just two) to the new window with four wires? Anyone that has done this already?


Regards,

Johan

This might help.

If not pm me.

Good luck,

Gerry

[jsoderbe]

Thanks, what a great forum this is! I just have to figure out how that compares to the wire harness in my 1973 911.

Do you know which one is the second stage? I figure that I only need the maximum one. !s the first stage just lower voltage or every other thread?


Thanks,

Johan

[86 911 Targa]

Originally Posted by jsoderbe

Thanks, what a great forum this is! I just have to figure out how that compares to the wire harness in my 1973 911.

Do you know which one is the second stage? I figure that I only need the maximum one. !s the first stage just lower voltage or every other thread?


Thanks,

Johan

pm me.

[flash951]

My rear-window defogger is not connected at all. Were on the window can I locate the wires?

[Grady Clay]

Remi,

The connectors are on the edges of the glass, under the rubber gasket.
There is a wiring harness that connect to the glass, pass through the gasket to a connector near the electric relay panel.

Johan,

Your ’73 should already be equipped with the rear window ‘relay’ controller. If not, the connector should be in the relay panel. If not, you can find a used one.

It is best to use the controller. The heating elements are fairly powerful and should not remain at full power when warm. The controller helps prevents overheating and consequent plated wire failure.

Before you install your new window, carefully measure each wire for continuity. You can do this by applying 12V power to the window and measuring the voltage in the middle of each wire compared to one terminal or the other. If you have continuity, the voltage will measure about 6V. If broken, the voltage will be 12V or 0V.

Best,
Grady

[flash951]

Thank you for answer. I have a 71 mod.

Is there simply 12V directly to the window, on/off, or is there a controller,?
Is it supposed to have the wires running to the relay panel on the left side of the engine?

[86 911 Targa]

Originally Posted by flash951

Thank you for answer. I have a 71 mod.



Is there simply 12V directly to the window, on/off, or is there a controller,?
Is it supposed to have the wires running to the relay panel on the left side of the engine?

For our '86.......

Here are a few answers to your question(s).

Why Porsche designed such a strange behavior for the 911/964 two stage defogger is a question that begs an answer.

The 993 models incorporate 15 minute on/off behavior (993-618-117-00).

The 911/964 models (1978-1992) are P/N 911-615-115-00.

As per the attached schematic, and technical bulletin, Relay #1 (the center element) remains activated when the defogger switch is pressed.

Relay #2 activates the upper and lower elements and stays activated until the the voltage drops below the minimum requirement of 11.0 Volts.

And, as you can see, only two wires are required to run this circuit, as the upper and lower elements are in parallel.

The ground wires location is a 10mm stud on the left side of the engine compartment. (G414).

Hope this helps,

pm me as needed.

Good luck,

Gerry


This note is from Hella.


This jpeg is my troubleshooting the circuitry.


Picture of the relay.