okay Jim, not to leave you hanging....the brake light switch controls both the tail lamp brake lights and the CHMSL....I assume that since the CHMSL gets it's power on a seperate circuit from the low stop lamps that I'll look in 8A and report back. You checked the fuse block right? Not trying to be funny.
For now I'd try to wedge the brake pedal and then check for power at the CHMSL wiring. I assume that the brake light switch is on the top of the brake pedal...but you didn't say that the other stop lights were out so I doubt that is the trouble....but I'll look in 8A....god I hate these electrical gremlins!
Tom