[Horokiwi_Hori]

My latest showstopper, after learning my heater core was leaking and replacing that.
Replacing the heater core required removing the dashboard, and unplugging a lot of connections, removing the driver's airbag (My car is RHD DCT 2013 e92 M3) passengers' airbag etc. I undid the bolts and lifted the drivers and passengers' seats back for better access. I did not unplug the seats.
I know there is a lot of opportunity to make a mistake on re-assembly and I was really careful but must have made a mistake somewhere. After I had reassembled the car, it wouldn't start.
When I insert the key the I-drive looks to be starting as usual, there is a small airbag error on the dash. Strangely, the light on the gear selector goes out. A larger airbag error lights on the dash. There is the large red airbag warning, a smaller red airbag and a red restraint warning illuminated.
The lights and radio work, seats go up and down but the engine will not start, no click sound, nothing.
I have checked the fuses but can find nothing. Checked the plugs and cables under the seats and on the airbags themselves. I'm really hoping there may be a diagnostic process I can try before starting to pull the Dashboard out. I'm not sure I'll find anything pulling it apart again. Any help would be great. Thanks to everyone who contributes to this forum.