Cougar wins. I couldn't stand it so I went back out in the cold frosty darkness with a bright mag light and had a better look - and it's confirmed, no only am I an idiot, but the cord from the floor actually routes up onto the seat, not the other way around. There are two separate connectors coming from that wire - one runs to the seatbelt, the other is the mystery hanger. I would now believe this to be as Cougar says, the power wire for such a seat.
Sitting down to spend some quality time with my manual...