AVDude,
If the wire goes up, how about peeling back the carpet and padding in the above room, and cutting open the floor to get a little more info. Might help. As for the voltage, use a regular electricians tester. They draw more power than hte digital units. The digital jobs autmatically switch to millivolts if your not paying attention.

If all else fails, Larry & I will come figure it out - with Sawzalls in hand!