I give up...

And please apologize my ignorance cudavert, I was just trying to provide as much info as possible to try and get a more direct diagnosis...

Oh no...wasn't trying to say you're ignorant at all. What I'm saying is that you mentioned the brake and turn signal circuits are both working fine, and that it's the TAILLIGHT circuit that is NOT. Taillights are basically 2 filiments, 2 "bulbs" in one. So I believe it's the taillight circuit, not the turn/brake light circuit that's inoperative here.