This is something that DomiRacer had made with the replacement Lucas 54033234 chainguard mounted rear brake light (stop lamp) switch that came on 1963-70 Triumph 650 twins T120 TR6 & 6T. Mustang motorcycles also used the same Lucas pull on type lever operated switch except Mustang didn't use this method of attachment. I had sold many of these switches to Allen Wenzel over the years and he had removed the spring clip assemblies. DomiRacer eventually ran out of our Taiwan made switch assemblies and I started ordering them from EMGO, except EMGO didn't supply the spring clip assembly with the switch. After checking currently, EMGO STILL doesn't supply this portion of the assembly, see the recent EMGO switch in the second photo. I bought these spring clip assemblies back from Allen years ago, so if you need to mount the EMGO or original Lucas 54033234 switch, here are your mounting parts. Lucas 315738 spring, F5412 (82-5412) & F5687 (82-5687) clip assembly. These are also handy for many other spring / small clip applications. 

My name is Tony Schanz, I formerly ran DomiRacer Distributors in Cincinnati, Ohio buying and selling vintage English, Italian, & German motorcycle parts, tools, accessories & memorabilia. DomiRacer closed 6/11/2013, but I still deal in parts, motorbikes, decals, advertising, photos, posters, & more. Please add my store, The Real DomiRacer, to your favorite sellers and watch for other rarities in my future eBay listings.