NEVER use an abrasive on solid state switch gold contacts. This will
remove the gold, which is soft, and cause inevitable switch problems. The best
way is to use a business card, or other stiff paper, and draw it through the
switch with light pressure. For additional help you may use some rubbing
alcohol or solid state contact cleaner on the card.
If for some reason you, or someone else goofed and filed away the gold
plating on the contacts, you will need to replace the switch and contact
points. These parts are easily available from most suppliers.