I had to take apart the switch and clean the rocker points and it made mine work. Don't forget to tighten the wire screws they will work loose in about two years and you think you have the same problem again.
I read this when I was almost finished with my IFR training and it looked like he had been with me on all of my flights. This is a good read and enjoyable.
http://www.campbells.org/Airplanes/Diary/toc.html