I’m looking for a how to or a wire diagram for seat harness plug on a Gen 2 and Gen 3 mini. As I want to swap stack Gen 2 seats with JCW Gen 3 seats.

 

I have actually just done this in my own JCW R56. You need to move over your current seat's electrical system (Yellow connector and little controlbox) and the seatbelt tensioner and then cut the yellow cable to the seat airbags. Then move everything over to the new JCW seats, put them in the car, and reprogram the Airbag module and disable the side airbags for both the driver and passenger. You can find tutorials on how to reprogram modules with NCSExpert all over the web
You need to disable "SIDEBAG_FAHRER" and "SIDEBAG_BEIFAHRER". This is atleast how I did it