Hey man, the green wire with the yellow stripe is for the brake light. I would trace it forward from the tail light as far as you can. Also, make sure you have the correct bulb back there. It's kind of a special bulb that does three things (tail light, brake light, flashes with signals). Should be a 6V 32/3 CP. I would check the filaments too to make sure one is not blown. Another possibility is dirty contacts in the switches inside the brake levers on the handlebars and work the brake levers. Get some quick-dry electrical cleaner at your local auto parts store and squirt it in there. Squirt some into the turn signal switch while you are at it. Hope this helps.