WARNING WARNING MAY CAUSE UNPLEASANTNESS!


It's a "make before break" type of switch.  If not required, it ought to be
for high-low beams.  

There might be a wee problem with this.  If you use both filaments at the
same time, the bulb is tossing out a great deal more heat than normal.
Possibly enough to shorten it's life span.  My Honda CRX cage [a cage that
really wanted to be a bike] had wimpy stock lights.  So we used to run
around with both beams on.  Made a mucho big difference - until both low
beam filaments died nearly simultaneously!  This was two weeks after
finding out how nice it was to use both beams.  I replaced the lights with
quartz-halogen lights and that ended the problem.