Heated Mirror Fuse blows, No Defogger

[Floyd B.]

I need some help understanding the combined heated mirror and rear window defogger system on my '96 convertible. When I press the defog button on the HVAC control unit, the heated mirror fuse blows every time. The indicator light below the defog button stays on for about 2 seconds then turns off. If I repeatedly press the defog button (with the fuse now blown), it does the same thing: i.e. the light goes on for about 2 seconds, then turns off. I get no heat to the mirrors or rear window defogger. The rear window defogger fuse does not blow.

I would suspect a short in the mirror heater circuit but why would that prevent the rear window defogger from working once the mirror fuse has blow? The service manual does not have a diagnosis procedure for this symptom so I don't know where to begin.

Thanx

[Floyd B.]

Re: Heated Mirror Fuse blows, No Defoger

Yes. I have the engine running when I perform the steps described in my original post. Thanx.

[Edward J.]

Re: Heated Mirror Fuse blows, No Defoger

Floyd, I suspect if the mirror (s) are fused one of the mirrors is shorted to ground , I think that if they are fused left and right that would make it easier. but the way to Dia. would be to un-plug them one at a time, which means removing the Mirror glass if possible maybe the SM will spell it out. must be something in the mirror grids, they will likely unplug on the back side of mirror.