Rear window defogger

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Bwana

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Do you have one and does it work? I have the switch (yellow button) in hand but not mounted into the dash detent yet. The under dash wiring is not immediately apparent. Looks like my wiring diagram lists it as item 101 and it has a single fuse from position #3 which, of course, doesn't match my fuse box. Looks like my "rear window heater" is in position #8.

I've checked the manual but have found no listing for the window resistance. What should it be? I figure I should make sure the window works before going any further. Can I just plug it into 12 VDC and see if it heats up?

Next step would be to follow the wires back from the window to the fuse box to be certain which connector to use. Which side does the wire feed? I'm assuming a local ground and only one power wire back to the fuse box. What color is it? The wiring diagram shows a relay to power it up, where is the relay located, it may help identify the power wiring.
 
Very slow

You cannot compare the action with modern cars where you see the action within 45 secs.
It takes several minutes and appears very weak, at least on my cars (the few times I drive them in conditions where it´s needed).

Check the wiring on the side of the rear window, where the flat contact of the wiring attaches to the male pin of the window wiring.

Also check the contact pins behind the yellow switch.
 
You can measure resistance and see if it is not infinite. I believe each trace is its own resistor so the most likely decay is that some traces work and some do not and thus
appears slower than modern cars. I believe there are products for fixing an open resistor
if it is caused by a short discontinuity.
 
also look at the rear window and see if the pattern has been interrupted - scratch through some of the lines.
 
i repaired the lines in my old 5 series (a long time ago) - i bought a little kit to do it, it was a little bottle of a metallic paint with a a flexible card (with a slot in it). no idea if these are still available since the defroster lines are so much better made.
 
Sorry, I guess I wasn't clear.

What's the resistance I should expect between the two leads on opposite sides of the rear window. This should give a good indication of if the window heater is any good and what my next step is.

Where is the relay located under the dash? I don't have the yellw button installed and I don't know if the wiring exists under the dash. If someone could post a picture of the relay it would help a lot in determining what I do or don't have currently in place. I can't find anything except the wiring diagram which doesn't show the relay location
 
rsporsche said:
Stan,

i found a repair kit on amazon that is made by permatex.
http://www.amazon.com/Permatex-1506...8-1&keywords=rear+window+defroster+repair+kit
Click to expand...

My guess is that a window with all its traces intact would read single digit ohms.
The more broken trace you have the higher the resistance, but if you have thousands or ohms or more it is broken.

Make sure your measure resistance with the switch OFF.

I am not sure where the relay is, but if you measure 12V at the window you do not need to know...

I like the method posted above of moving toward the inside of each trace and if the voltage does not start dropping then that trace is open.
 
Not quite a zombie thread resurrection but close. I'm still trying to hook up the defogger but am having trouble finding the wires. I found these loose under the dash, grey with red spots. Any idea what they are for? I can't find them on the wiring diagram.

P8291065.JPG
 
Grey/red is generally running lights. The rear Defrost switch should be next to the hazard switch and has the following: brown (2), green/blue (thick, from fuse block), red/white, black (thick). The black wire goes to the rear window
 
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