Chrysler Repair: rear window defroster control: 97 Breeze, climate control unit, rear window defroster

Question
Hi:
I own a 1997 Plymouth Breeze and recently the rear window defroster turns on and off by itself.  it will click on and off at different points during my commute.  sometimes it stays on for a minute then shuts off.  other times it turns on and off every few seconds.  I replaced the whole climate control unit with a used one from Ebay and it does the same thing.  then i replaced the relay in the fuse panel, same thing.  Any ideas??  Also the left side of the climate control doesn't light up when you turn the lights on.  I can see where the bulb is on the right side, but how do you replace the bulb on the left side that lights up the fan speed dial and head/floor/defrost selector?
Thanks Jason  

Answer
Hi Jason,
The timer that controls the relay is part of the body control module, and the switch at the climate control unit is connected to the body control module. There are two wires from the control switch: red and black/pink on pins 8 and 5 of the control unit (black 8-pin plug). Those two wires go to pins 5 and 19 of the body control module (white 22-pin plug). You could check those wires to see if one of them is grounded or intermittantly grounding which would be the same as if you pressed the switch to request the defogger. Specifically the red wire, when grounded, is what actuates the timer function of the body controller to ground the actuation coil of the relay. If the red wire is not shorted or intermittantly shorted to the red/black wire of to a ground, then the problem has to be internal to the body controller itself. The connection between the body control module and the relay is an "internal" conenection between the two modules that are ganged together under the dash (the junction block which contains the relay that you changed and the body module to which the junction block is attached). The other possibility is that there is a short in that internal connection between those two modules  The body module basically grounds and ungrounds the actuating coil of the relay to power and unpower the rear window defogger. So you need to check the switch to body controller wires, and then the internal connection in order to see which of those is faulty. When you separate the body controller from the junction block you should find some interconnection. Pin 13 of the relay socket is the connection to the body controller timer circuit. Finding neither to be faulty I would have to conclude that the timer logic circuit in the body controller is faulty which means finding another body controller.
On the light, I don't find any information on changing that. You may just have to dismantle that and use one from you old unit.
Roland