On this particular light, there is no switch. You would have to install it. It would hold a 26650 with a sleeve.
Other than the reflector this is totally empty. I could put a McClicky in the tail cap and make a sleeve for you. I sell these for $89 fully built with a McClicky and Pressed Fit PVC Sleeve for a 26650. They come with the New LED setup with deep reflector. This was just a project that I ended up never putting the guts back into after I machined it, and ended up using them in different customers lights. Check out my website for detailed pics.
www.ledfootcustoms.com