check connectors under the seat
do the reset airbag procedure found in the guides subforum.
If light still comes on it could be the loom in the seat itself trapped against the frame and shorting. It will require cutting the trapped bit out and re-soldering. Had this issue myself. Cost £40 to repair. Easy to get to as the seat covers have a zip at the back making access easy
best photos I've seen you take so far
Its a shame JapSpeed cant get their act together and get these exhausts to fit properly in the first place. Great solution though.
also added to Guides