Gremlins. Anyone pull the dash off? Maybe to put in a stereo? It's going to be tough to diagnose without getting my hands on it. If the third brake light always works, then it's not the brake light switch. And the only thing that I can think of that would interfere with the defroster is a lose wire right behind the switch, the switch itself, or a fuse which you say is fine. Pull the fron panel of the dash and see whats going on there. Let me know.
January, 14, 2012 AT 11:08 PM
Brake light relay at rear electronic module behinde the left side trunk cover is usually what fails. The relay is what controls the lower brake lights.