ok here we go.......
1: Your switch should look like this when removed from the distribution block
next look it over you will see where it has tabs that lock the top part of the switch cover onto the switch itself, insert a knife or other object in the seam and pop it apart on both sides as shown here
when apart it should look like this
and the pencil in this picture is poiting to the contacts you will want to clean,, look like really tiny disks...if you press the little copper tabs in the center you will here it click, and that is how it works so just take it fron there
thats the best way i know how to describe it......

if you have trouble, reply here i will check back, to see if i can help more..... this should fix it thogh i would bet it is just corroded.. If not you can order the switches but they are like 15$ i just replaced all mien cause the little arrows on the switch were starting to not be visible......
jason