Ian,
Does that one also has a P in white engraved on the top? I never see them much at jumbles, so think the postwar ones are different.
Rob,
It's written in the "Motor Cycle" of around November 1944, as an official WO modification, but cannot find (for some time now), the whole 1944 stack of those issues, might have lent them out I fear, but I remember the text from the article very well, have written it down but in Dutch, will translate and post it here later. Last August I went through all of the other wartime magazines, both the Blue un and the Green un, and found one article from 1943, that dealt with the same problem, but it's not the one we need, some friends are building late war machines, so I wanted to give them all the info, hopefully it will be found soon.
But two pictures of the wiring diagram for the under saddle switch attached here.
Cheers, Lex
email (option): welbike@outlook.com