These high-mount brake lights notoriously go bad. Pull it out, put a volt meter on it, and have someone hit the brakes. IIRC, you'll need to replace the whole assy if bad. I think I used some rtv black to ensure a weatherproof seal.I cannot find a reason for this strip of (lights?). Whether I am in Park, Drive, or Reverse, day or night, they do not do anything. I was thinking they might be some kind of reverse light, but they don't light.
Let the chuckles begin...
Jim
Oh crap....forgot to add the pic. Let me try...