Hi Pat..Assuming you are talking abut a WD bike,you need to use the arm from a 4 position military switch as opposed to the 3 position 'civvy' one..
The recess in the base of the arms are in slightly different positions for the two types and if you swap them the arm won't line up correctly with the marked positions on the switch..
I think the following link may be the Gizmo that Ian is referring to. I bought mine from this site, Al Osborn the NOC's Electrical Specialist. So much easier than messing about with flimsy bits of paper and, more importantly, leaves both hands free.
Hi Pete..This seems to be on the end of the wrong post...?
I bought mine from a company in Cumbria and although broadly the same thing, it has an additional useful feature..an audible as well as a visual 'tell tale'.
So, there is no need to actually be looking at the unit as you move the mag armature round...