BRAKE light HELP!!
 

I have a 2004 Excursion 6.0 Powerstroke that I purchased a few weeks ago. Tonight I was driving behind my wife, who was driving the Excursion, and I noticed the brake lights didn't work (now I'm not sure if they've ever worked since I bought it). When I got home, I checked every fuse that had "brake" in the description. None of the fuses I checked were bad. All of the other lights (turn, running lights, etc.) are working fine. The Ex has 3 brake lights (one on the top of the rear glass). I've read some places about a stop light switch. Could this be the problem? Any other things to check. If I plug in a trailer tomorrow and the brake lights on the trailer work or don't work, does that help diagnose the problem? We are supposed to leave for vacation tomorrow, and I'd really like to have brake lights!! HELP!! THANKS!