The dimmer switch lives in a very hostile environment- - - -right there where splash from the front wheel lands. If you're in an area where a lot of salt gets used on the road, all sorts of junk gets sprayed onto the switch and its wiring. Start looking for problems there.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!