Odd brake/tail light problem

Problem solved! At least, temporarily.
I did as you suggested and tested the brake switch with power - it works.
I unscrewed the fuse box mount to get a better look as I followed the pink wires back and found... the palm of my right hand slapping my forehead. Nikolai Tesla over here seems to have missed the fact that there was a blown 20A fuse. I SWEAR I looked closely at the fuses first and did not see one blown.

But now everything is working as it should except for one small thing: the left blinker is still much slower than the right when key is on but engine is off. With engine running, all is normal.

Thank you all so much for your help. I have no idea why the fuse blew in the first place and will keep an eye on it, as well as keep some spares in the glove box. And now I know that the brake lights are on a different circuit than the others, too.