Regarding that bicycle lighting kit on eBay...the brake light switch mounts on on the rear brake cable, just above the screw on the brake that holds the cable. When you pull the brake lever, it pulls the cable, and the switch hits the cable stop on the brake and closes. I hope you can understand what I'm saying; my powers of description leave something to be desired. Suffice it to say that the switch is clipped onto the brake cable, and when the lever pulls the brake cable, the switch presses against part of the brake, closing it.