Satch,
I just got done troubleshooting my rear door popper and what I found may also affect your defroster.
If you open the jack cubby on the drivers side of the VX and look at the back wall of the cubby you'll see two disconnects for the wire looms heading from the rear of the VX to the front. The one on the bottom is the loom with the defroster wire, and the license plate lights. If you follow that loom to the back of the VX it should pass through a rubber grommet and that grommet should be seated down in a niche in the metal plate that it passes through. If it isn't then the loom could be in the way of the path of the rear door stop. When you close the door the stop swings into a cavity behind the brake light and passes through a hole in the metal plate that the wire loom passes through. My loom was out of the niche and the stop kept crushing it against the metal plate until if finally cut my door popper wire in half. It had also worn through the wire insulation on one of my wires heading to the door, but luckily I hadn't had any problems yet.
I'm wondering if maybe your wire is frayed and may be shorting out on the metal plate that the loom passes through. I can take pictures of everything that I'm talking about if you think it will help.
Good luck.
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-Douglas Adams, Mostly Harmless