That’s brilliant - thanks people, after you’ve told me what it is and then going back armed with my new knowledge it is currently in a non-functional state.
I’m learning to look at something, take a picture, think about it, search the forums to see if anybody has posted about it before, think about it and return to it to take a look - then if necessary post the question asking for help from the wealth of knowledge available here. BSA ownership I’m finding is very enlightening, interesting and more of an experience than “just riding” - superb