I've put the camera under the passenger seat and found some interesting connectors and cabling.
In this picture taken from the under front of the seat you can see tree cables with connectors each one coming out of one black flexible wire tube from the ground. Two cables/connectors are connected and one not is used:
In this picture taken from the under back of the seat you can see a yellow silicon flat cable running towards the back of the seat, disappearing upwards in to the seat's back support. Could not guess where that one is going or used for:
And in this picture you see a flat pcb cable with the name AISIN, coming out of the seat part of the passenger chair.
I checked the drivers seat and the same connectors and cables are present, only not the AISIN flat pcb cable. So I'll guess this is the seat belt warning sensor.
Possibly the not used white connectors should be connected to the seat heaters, when installed of course. Like the picture Rickl posted.
Then this is what Dr. Dyno wrote; the cable harness is fully wired, but not all options have to be installed and connected.