I'm trying to get my rebuilt turbo swapped vert ready to be driven daily. My rear defrost is not working. Here is what I've checked so far:

1. I've checked voltage on the rear window harnesses/plugs and get nothing when defrost switch is turned on.
2. I've checked voltage at the defrost fuse on driver kick panel fuse box. I see voltage when I turn the switch on.
3. I've checked the fuse and it has continuity

I'm looking at T-24 and T-66 thru 68. If I'm seeing voltage at the defrost fuse do I need check pins on the switch and timer? Seems to me that if the fuse sees voltage when the switch is on and the fuse is good then I should be checking the relay and the two grounds in the circuit diagram on T-67(below). Also what is the second fuse going to the timer? Is it on the kickpanel fuse box? Also, also...I haven't been able to track down the diagram showing where the two grounds are located on the car. I'll keep looking but if anyone knows the wiring diagrams better than me I would certainly appreciate the help.



On the wiring diagram, Z-88, am I looking for voltage on both B/W and B/L correct? When the timer times out the B/L will open which will open the relay and B/W will no longer see voltage either, whether the button defrost button is pushed or not.


Possibly related, for a time the indicator light on the defrost switch was spotty. It would not illuminate every time the switch was pushed. Sometimes it would only come on while the button was pushed, sometimes not at all, sometimes it would come on fine. Now it illuminates everytime, but no defrost on the rear window.

 

the ground is the simplest, i think. you can take the ground side tab off the window (carefully! they can pop off, and be resoldered), and see if it goes to ground.

if the defroster light was intermittent i would suspect the switch, but the relay might be easier to check

the relay, which lives next to the antenna, should have power on one pin, and continuity to the defroster on another, and then with the key on, there should be power on another pin. turning the defroster on should ground the 4th pin. if it doesn't, you need to look at the switch

 

I figured the switch also, what with the intermittent light. I swapped a previously used and good switch with no change. That's when I started looking at fuses and such.

 

Was the back window ever tinted? The grid could be damaged

 

No, never tinted and no broken lines on the grid. IIRC I checked continuity across the two pins when they were unplugged. But it's been a few months since I last messed with it and I did not take notes. Next time I'm in the car was was going to check it again.

 

don't the wires on the window go down and get connected..again.At the inside of the car?
something like a patch cord in between the window and the body harness?
I'd check that connector for corrosion seeing that you get intermittent connection.

 

I haven't traced the wire to ground yet. Convertibles aren't too friendly with all the molding behind the seats. You may be right on it looping back into the body harness.

I looked at Z-88 with it on full screen on my monitor rather than windowed. It references what I believe are two wires coming off the defrost heater going to I-05 and another going to I-06. Legend at the bottom looks like I-05 goes directly to ground. I-06 reads "Connector between rear (R) and Rear no. 2 (R2) harness." and then going on to what I believe is ground #7.

 

Bahaha I went out to test a few things. Put a meter on the ground side of the defrost heater to see if it is in fact grounded....I popped the hood and was reminded that I pulled my battery box and battery so that I could make a new battery box out of some scrap stainless sheet metal at work.

 

I looked at resistance on the ground coming off the heat strip, it's at 5 ohms. I simply took a jumper wire put it on my neg battery terminal and put my meter in series between the jumper and the wire going to ground (passenger side). I started tracing the ground to it's termination and haven't found it yet. It has a connector between the vert top and headliner which then runs down passenger side across the taillights and heads back towards the front of the car on driver side. I got as far as the antenna and relays on the side of the trunk before it got too imbedded in the harness to trace it without having to open up the wiring.

As a reference I ohmed out the actual heat strip and it's at 2.something ohms.

At that point I figured if I took a jumper wire and grounded the passenger side terminal directly to the neg battery terminal I'd see/feel some heat on that strip....nothing. I checked voltage across the two heat strip terminals and it's still showing nothing with ground side grounded directly to the battery. and key to START

I never found two ground wires referenced in the FSM

 

Found it, antenna fuse had popped. Put a fresh 10a fuse in and I see 10v across the heater terminals. Take it out and I see squat.

I thought I had checked all my fuses but I either missed it or it was still good while I was getting intermittent lights on the defrost indicator/switch. Either that or I had a ground loop problem on my aftermarket stereo and that's what ended up popping my fuse and/or the ground loop caused my intermittent switch/indicator and then the fuse to pop.