Just a quick update. I finally got a chance to start working on the problem last night and the first thing I noticed was that the rear passenger side footwell was soaking wet. After pulling up the carpet I can see the wire channel that pesuazo's post pointed to. Didn't get any further but I'll need to take a look at that wiring. And of course now I need to figure out where the water is coming from!
BoB

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1988 300TE
1991 Miata