Brake Light Problem

My driver side brake light is always on. This is only when I turn on the lights at night also. The other brake light and the third eye still come on when I depress the brake pedal but they do not stay on like the driver side. I have checked the fuses, replaced the brake light housing for the driver side, and I have replaced the bulb. Nothing has worked. What could it be? If it is a short, how do I find out and how do I fix it? I could use some help because I suck at solving out electrical problems.
 
it must have constant power going to it some how. i would just use a test light and test wires on both sides of the car(the one that is broken compared to the one that isn't) then trace the line that is hot and find where it is getting its power from.