Brake light always on, help?!?!

The problem began intermittantly, now it is at all times. The top center brake light is not affected. I have removed the stop lamp switch from the brake pedal and cleaned and sanded the contact points inside the switch. I removed the lamps and inspected them, nothing appears to be amiss. I've been searching many various forums, and I see this problem posted occasionally, but nobody has posted a definitive fix. Any help here? Thanks.

replace the switch with a new one.