Gary,
You should find 12v on the large red wires that attach to the center posts of the curtain switch. Suggest that you not use coax shield for ground. Run a wire from a ground under the dash instead. I usually hook to the steering column bolts.
The TV boost power comes through a 15A fuse. It should be located in the bedroom closet breaker/fuse panel. It should be Circuit 12, labeled "Start Boost and TV Power Feed." I suspect it also feeds the curtain motor.
BTW, a plastic rod is a lot simpler, faster, and cheaper than messing with the motor. Replacement cost was north of $300 when I checked.
Steve
Steve