****In desperate need of Tech help with my rear defrost****

palma411

New Member
Mar 21, 2010
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Houston, Tx
I own a 1988 Mustang GT that I am in the process of restoring, but the problem is that it came from factory without a rear defrost window and I am going to replace it with a rear defrost window (glass not on yet). I have installed the switch on the dash for the rear defrost and have insatlled the relay that goes under the dash to the plug and now the light on the switch turns on. The problem i am having is that I have the a solid gray with a yellow stripe wire at the rear by the hatch and when I turn on the switch I get no power to the female plug that plugs into the glass terminal to activate the defrost.

Does anyone know if I am missing another harness somewhere or what the problem could be? I have the car in pieces so It would be easy for me to locate a wire, I even have a Factory Ford wiring schematic for the car, but only shows me the wiring to the swicth and the relay at the dash not the rear.

I would REALLLY appreciate any help possible here, I am desperate!!!!!
 
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Yikes. I don't know the answer to this. I would think there is another harness somewhere in between, I just don't think it's one solid wire front to back. But I could be wrong.

You've checked for power at the window, did you check for power at the relay?

I've got three foxes and none have defrost so I'm pretty much lost as far as the route of the wire. Just make sure you have power at the start since you don't have power at the end.
 
Hey thanks for the reply, but yeagh I have checked for power at the relay but nopower at the back harness plug that plugs on the side terminals on the rear glass. Man I have no idea what to do anymore.....im at a total loss here.

Any help WOULD BE GREEEEEATly appreciated by anyone!!!!
 
Yes, I checked this wire the BLK/Y and it does have power and when I turn the defrost switch on and the light turns on I hear the relay activate (click) and when I turn it off i hear it click again. I was told by an auto electrician that there is a GRY/Y wire in the back that is supposed to power to defrost, but this is the wire that has no power when i activate the switch.

Have you had this problem before?
 
Well I called Ford and they sent me a wiring schematic and apparentky what i am missing is a female 4 prong connector that plugs under the dash that is by the relay with a solid purple wire, gray/lb, blk/y, and a brn/lb wire and then when it connects it coinverst to a single one wire which changes to a gry/y wire and this is what powers the rear defrost. WOW if anybody has one of these and is willing to part with it please shoot me an email .......thanks everyone for your help!!!!!!!!!!!!!!!!!