BackInBlack

New 951 owner here.

The rear defroster doesn't work. I tested per Clark's garage and got 12v on both sides. Unhooking the wire from the passenger side I supplied a ground to the connector that connects the hatch strut to the window grid. I can't really tell (warm day) if the deforster was working, but the wire got quite warm (to the point of discomfort) in my hand in about 30 seconds.

Now I undertsand that the grid is a resistor (like a toaster) and likely some significant current is being drawn, but should the wire get warm like that? It's pretty small gauge, compared to the + side. My "school" says the - side should be the same gauge as the + side.

Also...where does the - side physically connect to ground? It goes into the grommet and disappears behind the trim.

BTW...this seems like a great forum.

Techno Duck

I had this problem on my car as well. Tested every component and all said it should be working, but it wasnt. I touched the wire on the drivers side (12v feed) and it was extremely hot, to the point if i left my hand on it any longer i would have gotten a nice burn. I took the wire off and tested the resistance across it and was getting values from 50-100 ohms. I peeled the insulation off which revealed severely corroded wire. I made a new jumper wire and replaced it..and can see out the rear of the car on those frosty nights now. Make sure to use the same, or smaller gauge (thicker) wire.

BackInBlack

I'm pretty good with wiring, but where do the passenger and driver's side go (base of hatch strut into trim panel). Or did you just replace the strut to grid jumper?

Good tip on the corroded wire. That could definitly increase the current drawn for a grid of "X" watts. The voltage drop while operating could make the grid ineffective as well.

V2Rocket

the wires creating resistance is what causes them to warm up.

Mighty Shilling

I'm interested in this too. my 924 I can't see out the hatch on frosty mornings until the cabin warms up enough to melt the frost... which generally happens as I'm pulling into the parking lot at work.

BackInBlack

I'm still interested in knowing just where the passenger side wire goes to get it's ground after it goes into the trim through the grommet. Also still surprised it's such a small diameter wire...and with a 30 amp circuit no less. The + side is considerably thicker (at least the insulation is) and my electrical rules say they should be equal. I know I'm not comfortable with the wire getting that hot. The heat should stay in the grid for the most part. The wire may have reduced ampacity due to corrosion. Kinda weird using the shock as a conducter in my mind.

I'll let you know how my progress goes. Not regularly frosty around here that often to really acid test it as I go. Unless it's quite chilly out, I don't expect to be able to feel the grid heat much, but I could be wrong.

Car went in to get the A/C diagnosed today. Gonna need a new compressor and switch over to R134 at about $900 including the diagnostics. Not unforseen really.