Why does the engine die when I give it some gas?

Why does the engine die when I give it some gas?

motorcycle is suzuki gd110. if the headlights are off, the engine won’t start. if i turn on the headlights, the engine will start but will stall when i give it some gas. it will only run if the headlights are on full high and the turn lights are on. horn is weak, turn lights don’t blink. no power to any light when engine is off. rectifier has been replaced and battery is fully charged.