A motorcycle headlights burn out frequently at high engine RPMs. What is the most likely cause of this electrical issue?

1. The voltage regulation circuit inside the regulator/rectifier has failed, allowing charging voltage to rise too high.
2. The headlight bulb wattage is too high for the stator capacity.
3. The stator exciter coil is shorted to the engine ground.
4. The battery is completely charged, forcing all excess current to the headlight bulb.