The rear brake lights will turn themselves on

The rear brake lights will turn themselves on after the truck is sitting idle for many hours at random times. I am told by the mechanics at Sears that the Brake Light Switch needs to be replaced. But while researching the problem I have found there is also a relay with and fuse that control the brake lights. I am not sure what to do, as I woke up yesterday morning to a dead battery because of this issue. The battery and alternator are new, so I know it is not due to these items.