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Read Defogger problem


Guest orrville69gs

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Guest orrville69gs

I have a 1994 Century wagon. When I press the brake peddle the rear defogger swith turns on. The brake light also does not work in the window nor does the defogger. I have looked for a short but I haven't been able to find one. Has anyone seen this before?

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Never heard of that one, but first place I'd check is to see if someone used an incorrect bulb in one of the sockets. I don't think there is a way to do this in the newer cars but a wrong bulb causes some really goofy electrical stuff to happen. My buddy put the wrong bulb in a 69 taillight, brake lights would not work but when ya hit the brakes the dash lights would come on.

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Look for a GROUND issue, rather than voltage supply issue or "short". In many circuits, when a particular circuit loses its ground, it'll backfeed into a circuit that has a good ground, which can activate some unusual lights or circuits. Many circuits have only a supply wire to them, using the body of the place they go for the "chassis ground". So the switch for the defogger isn't actually turning "on", but the backfeed from the other circuit is bypassing the switch to make it work.

For example, when a front turn signal circuit loses its ground (a ground wire on EACH side of the front of the vehicle), it'll backfeed through the turn signal indicator (for the particular side which lost the ground) in the instrument cluster . . . getting to ground that way. At least that's what happens on one of my GM cars.

As the problem is in one area of the vehicle, that's probably where you'll find the loose or broken wire. As both of the inoperative items are in the tailgate, it could be that a wire has broken in the flex area of the harness going to the tailgate itself. I suspect that if it was a "chafe" or short, you'd have a fuse blown.

Keep us posted, please.

Just some thoughts . . .

NTX5467

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