My 1999 F150 left brake light doesn't work, can anyone help?

My 1999 F150 left rear brake light doesn't work. ALL other lights work;
front/rear turns-parking-hazards-reverse-license plate-head light-fogs....
Literally every other light works, except my left brake. I've replaced the bulb,
socket, pigtail, multifunction switch and checked all the fuses and have a
good ground. (Checked by connecting to the body and thru a known ground
wire running a bulb that was burning at the time.) When I jump a wire from the
right brake to the left, it lights up when applying the brake pedal. BUT the
LEFT turn signal activates when I engage the RIGHT turn signal. Remember,
the left turn works fine while wired normally and when the jump wire is
installed to the right brake. I'm at a total loss. The only thing I can think of is
the brake light switch on the brake pedal??? But does it supply power to
BOTH lights thru a common wire, or are they wired separately? I'm
exhausted. Anyone have any ideas on how to fix this?

Thanks,

Dan H.