I have a set of the standard 70's triumph/bsa ones fitted to my S/R, however when I removed the handle bar fairing I was left with the dilema of not wanting to drill a hole in the headlamp brackets and did not wish to drill the thread out in the headlamp, so I turned some alloy down stepped with a small hole drilled right through for the wire, a cycle thread tapped on the small diameter for the headlamp and larger hole on the other larger dia. end with a BSF thread tapped inside for the indicater, sorry having a bad memory day so cant remember thread sizes,the jobs a good one, just have to prove the alloy will stand the riding treatment, will let you know after the John Bull rally.
The rear ones are fitted to the pannier supports fitted to the rear carrier.