Hey guys, I had one of these in my 71 westy. I found that if you take a light switch knob (one that lights up) and unscrew it, it will screw into the center of the mystery ring and light up and it becomes a switch. if you pull on it and the wire is hooked up I the back. So basically it turned out to be a switch that was missing it's pull knob.

 Maybe I am wrong but this is what I learned by trial and error.  Hope it solves the mystery.