Well, turns out that by using a fuse tap on fuse 41 to power the O'Reilly led amber lights on the grill, it somehow affected the tail light. I decided to remove the tap and re-installed the fuse to see if that was the cause, sure enough, the tail light is working.
I'm thinking somehow the minimal current drop (taken by the amber grill lights) caused a malfunction.
I followed the instructions from someone in this forum to tap fuse 41 but that caused the problem.
Very interesting, indeed.