In case some detailed operating information is of interest to anyone, may I say that, although I can't speak with authority on brake van vehicle characteristics, from participation in signalling in the late 1960s, AFAIR, partially-fitted trains also carried side-lights ; 'unfitted' referring to trains which had no braked vehicles at all apart from manned brake vans.
And also that, side-lights were to show white lights forward, but in my area at least (where the old Rule 120 applied without amendment), the colours that they were required to show to the rear were not so simple, having to be changed en route by the guard if / when necessary. : -
- On Main, Fast and Single lines both sidelights were to show red to the rear.
- If there was one additional running line in the same direction (e.g. Slow, Relief, Goods lines) when running on it, the train's side-lamp nearest the Main / Fast line was to show white rearwards; the other one to remain red.
- If on a third line in the same direction (or a fifth, etc.), it was back to both side-lamps being red.
- if on a fourth line (or sixth, etc.) it was again to be as for the second line; one white, one red.
I believe, over time, that while some brake van side-light lamp brackets were able to swivel, thus catering for lamps which showed their red and white colours in different directions; other side-lamps did not need to be swivelled because although they always displayed white, they also had a slot into which a red 'slide' could be inserted to provide the required colour flexibility.