Targa, dual stage, defroster circuit help request.

[bobmagyar]

Hello,

I am hoping to sort out the rear window defrost function on my Targa. The car has a dual stage switch. First off, I don’t know what that means in terms of function. I guess that’s question #1!

Where the wires come from the glass into the engine bay there are 3 wires. 2 Red and one brown. When I measure the resistance, I get 1.5ohms between the brown and each of the red. Between the two reds I got 3 ohms. Does anyone know if these resistance values are correct?
My defroster wiring harness has 2 red wires and 1 brown. It would seem obvious that I should connect red/black to red1, red/white to red2, and brown to brown. I don’t take this for granted since I am not sure if the resistance values are in spec.

When I activate the switch only the red/black wire from the panel receives power. The red/white one never receives power when the switch is in either stage. Perhaps my relay is not correct or working properly?

If someone with experience with this circuit could chime in it would be greatly appreciated. This has not been hooked up in over 20 years and it sure would be satisfying to make it so!

Thanks in advance!

Bob

[Scott A]

I’ve always thought the two stage was this. One stage does half the wires, second does even more. But I never tested that.

Sadly, It is very common for the wires in (on) the glass to be worn and not connecting, from sun damage or other.
Next it is very common that in 50 years that the wires on the side of the glass are often disconnected. If you are lucky, inside the car, you can flex back the rubber, halfway up, and see if you see bladed connectors, and inspect.

I would use a test light for most the testing.

So even if you find the correct wires going to the glass, it may not work.
You might have to check those wires.

It can be a long trouble-shoot.

Some good news. The rear glass is easy to reinstall, best done on a summer day in the sun. (yet, most of the time has to be cut out)

And there is the relay in the rear and a fuse in the rear. #3 fuse (lowest one)

Update: Sorry just noticed ‘targa’ not so easy to remove or install.


See this link: it has helpful info, but also states the difficulty.

https://forums.pelicanparts.com/pors...-location.html

And another link

https://www.early911sregistry.org/fo...-is-this-cable