89 cheynne brake light problem

i have an 89 cheyenne motor swaped out, tranny rebuilt,   left rear brake/blinker stop working on me. its not the bulbs or fuse and there is power running to the back right tail lite.  can someone throw some suggestions at me as to what the problem is.

I have a simular problem. my blinkers work, my trailer lights work, but my tailights and brakelights dont. i did an engine and tranny swap like yourself. and i still havent figured it out.
 
if you figure it out elseware. please post me with an update and ill do the same.