as everyone else stated u probably damaged the switch when you swapped handle bars. i did the same thing. instead of buying a new switch i superglued a piece of cardboard where the lever hits the switch. this was able to close the gap and it worked fine after that

 

Start with the simple. First check the bulb, sometimes the tail light filament will break and short. This causes the brake filament to stay on. Save your self hours of frustration, replace the bulb first.

 

wow lots of great suggestions buying a brake switch tomorrow thanks all

 

Hey all - having similar issues. When I push that front brake switch in I also lose the running light. Doesnt seem normal to me. Did this with the bike off however, not sure if running lights dont work unless bike is running....

 

Just found this. Probably a good place to start. Im a f**king idiot.