why is mr. gimmie talking about signals? the op is clearly talking about the brake light. the "running lights" he mentions is the natural state of the tail light, the second filaments clearly aren't lighting.
first just check the bulbs, maybe the brake filament is broken in both, though I doubt it.
what I actually suspect is that one of your switches is closed and you aren't seeing your running lights, you're seeing your brake lights.
unplug one of the connectors at the front brake and see if the lights dim, if they don't, check that the rear brake light switch is working properly, it could have malfunctioned. you could just unplug it to see.
if the running lights are working, then there isn't a ground issue, as both the brake light and running light share a common ground.