After messing with it for a few hours, just when I was ready to start pulling the whole dang assmebly out, I stumbled on the problem. The wires which run from the motor to the big connector were getting pinched by the mounting bracket and were shorting out! It had nothing to do with the rain or the wire binding! (sigh) So I put on some electrical tape, used some spare weather stripping (to create a buffer), and reinstalled. Works like a champ.
Thanks to everyone for all the suggestions. I put them all to use until I stumbled on the real culprit.
