Thanks Max and Norm,
Unfortunately I don't quite follow, as I was hoping to just get a confirmation on the wiring in my diagram, on which I marked the key positions in red. Any other diagrams just add to my confusion.
The old Harley control switch has OFF/RUN/START. I would have thought this setup exactly the same, unless I am missing something?

Failing that, these control switches are a dime a dozen on ebay, which should do the job as the switch is said to be a "kill switch".