Ezmoney is right about the tail light, but there is not a voltage regulator in the stock electrical system. In a sence, the head and tail light are the sole "regulator" in the system. Say your head light burns out due to the life of the bulb, your tail light will follow, and vise versa. This is because of the excess voltage available. Now you could add a higher wattage head light bulb, it just wont be as bright.
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82 YT175
PK Racing Pipe
DT175 Jug
82 YT175
DG Head
Bassani Pipe
Rear suspension
YZ80 Forks