I forgot to mention in my earlier response that you'll probably find when you get it open that all the wires are intact at the switch. What usually happens is that one of the wires is actually broken inside the cable where it constantly flexes in use ie right where it bends going into the switch. That being the case you'll need to cut the cable back about 50-100mm to remove the bad bit and re-terminate it completely.....
Doug
February 2007