It depends on when your BSA was made. It could be found on top of the rear number plate holder, also on the top of the toolbox and just below the wd tail light. I have pictures of all locations if you need an example.
My bike was built late June 1940 Henk (frame no. 22280). I have the MT110 rear light which as you are aware is easier to get hold of than the MT1130. So what would be position in this case?
