Rear defrost/wiring problem

[jrmoen]

Hi Everyone,

I’m having a problem with my ’95 Bonneville and hope someone has an answer. The rear defrost button comes on by itself and kills the engine. When this happens I crawl under the dash and pull the fuse then the car would start back up. Well, lately this doesn’t seem to work. The other day I pulled the fuse and the light (on the r-def) wouldn’t go out for about 20 minutes, then the car started. The next day I was driving it and the RD light came on and the car died. The strange thing about this was I had the fuse pulled and the RD light still came on and once again I had to wait about 20 minutes till the car would start again.

What would cause the car to die when this comes on? Why would the RD light come on with the fuse pulled or come on by itself at all? I noticed the RD is connected to the hot/cold knob on the dash, could this be part of the problem?

Thanks for the help.
JR Moen

[LMP]

Originally Posted by jrmoen

What would cause the car to die when this comes on?
Why would the RD light come on with the fuse pulled or come on by itself at all?

THe fuse will not disconnect the RWD: it just disconnects the feed to the button. This button trigs a relay and the power feed to the relay is through a separate circuit breaker. ALso, the feed to this button is on same circuit as ignition.
The "RWD relay" is in fact a solid state timer and an electromechanical relay packed together. I think this unit (located in the "convenience center" probably under the glove box...not sure for this model) is the culprit, and possibbly has an internal short that sends erratic commands to the relay and that shorts the ignition circuit at same time. I'm just surprised the fuse does not blow out!

I'd pull the RWD relay off and see what's next.
THis circuit is "typical" of pontiac.
www.avigex.ca/xport/reardefogger.jpg