As luck would have it, I had mine (92 400e) apart yesterday. The pigtail comes from under the carpet and up to the seat. There are two minor connectors that are in the middle of the wires that are pretty obvious. The thick bundle you were referring to goes into the center of the seat, and to two connectors mounted to the seat hardware. If you loosen the vinyl cover under the front edge of the seat, you can see them. Fortunately, I ended up not having to disconnect them, but you can do it from the front side. I don't think there is a connector under the floor.