I found a simple way to add a brake light switch to a bicycle brake lever. Specifically, this is for a mountain bike lever that pulls a cable for the brakes although it's possible it could work on other levers. I would not try this on super lightweight brake levers as the metal might not be thick enough to tap threads into and it might weaken the lever excessively. The switches I used can be found at radio shack and are mini momentary pushbutton switches that are normally closed (N.C.). The tools you will need are: allen and/or box wrenches/sockets, duct tape, half round metal file, pencil, tape measure, center punch, drill and bits, 7mm fine tap and tap holder, wire, solder, soldering pencil, heat shrink tubing, heat gun and electrical tape.