A few more pictures...
Light guide snapped in the correct place.
Installing lighting in Kato RhB EW-I coaches by Jim Easterbrook, on Flickr
Installed.
Installing lighting in Kato RhB EW-I coaches by Jim Easterbrook, on Flickr
Excessive light shining through coach end doors.
Installing lighting in Kato RhB EW-I coaches by Jim Easterbrook, on Flickr
Light spill reduced...
Installing lighting in Kato RhB EW-I coaches by Jim Easterbrook, on Flickr
...by taping over the end of the light guide.
Installing lighting in Kato RhB EW-I coaches by Jim Easterbrook, on Flickr
(I tried aluminium tape instead of black insulating tape to see if it would reflect a bit of light and make the dim end of the coach brighter. It didn't have any noticeable effect.)