Need help with brothers 04 Stratus

Ok, my bro has an 04 Stratus with a brake light problem that I will be looking into in the morning,so I need some ideas.

The problem:

The drivers side brake light does not come on when he hits the brakes. The passenger side and 3rd. brake light up just fine. With the running lights on,all bulbs light up,but the same thing happens.I can see the bulb itself is on when his running lights are on,but when he hits the brake pedal it does not get brighter.

I cant think of what it could be,all other lights work fine,and the bulb lights up with the rest of the running lights...hmmm...any ideas are greatly appreciated!
Author: admin