I fitted the new steering wheel slip ring this afternoon and the horn now works. The airbag warning light is on - maybe that needs resetting?
While checking that all lights etc work for registration inspection I found that the windscreen washer water pump has failed so I swapped it with the one out of my other 318is to get passed pink slip. Will find a replacement later.
I drove the car a little within my own driveway and it seems to be running well, aside from a bit of a funny idle every now and then (runs rough and low rpm).
All is on track for the fitting of the new automatic transmission and registration in the new few days! Finally.