Hi Rob
Glad to hear your engine is running well.
I used the original BMW brake light switch. The circular hole needed to be modified into a square hole with a little additional groove:
http://www.flickr.com/photos/3310545...in/photostream
http://www.flickr.com/photos/3310545...in/photostream
Whether this was the simplest solution I'm not sure, but it seems to work OK.
Cheers
Tim