OK, it turns out the grey cable is a piece of 1950s, Levitt-installed NM. Gotta love tract houses. That cable disappears under a seam in the tar-paper, to a receptacle in my room I assume (my room is on the other side of that tarpaper.)
However, I still haven't figured out where that old fireplace cable (dark brown one) goes. I have a feeling the previous owner/handyman had an outlet in the way of said fireplace, ripped it out and thought "why not install some fans for my new fire-hazard..."
Ian A.
