[grumpyunk]

The brake lights will only glow when the ignition is switched to ON. They use battery power, as do the headlights. If you have no light, the most likely spot to look would be where the switches(F & R) get their power as they are fed separately. Likely inside the headlight bucket. Find the wires that feed the switches - one to power(B+), the other to the F&F light sockets. Both switches use ignition switch controlled power.
A quick check is to see if you have power to the rear brake switch, kind of out in the open and easier to access. Check for power on one wire with the ignition ON. If no power, follow the power wire back to its source of power.
Ignition switches of old had a 'park' feature that would send power to the rear tail light, used to mark the bike presence in the dark in narrow allies/ways. The position was separate from OFF/RUN. FWIW.
You could also check for B+ at the ignition switch, both IN and OUT.
tom