Is this the schematic you have?
http://faq.ninja250.org/wiki/Headlig...cuit_schematic
This could help too...
http://faq.ninja250.org/images/f/f4/..._Schematic.pdf
Yeah it is pretty simple. Think it could be the diode? Now I think about it, I doubt it.
Could it be a bad socket? Maybe cracked causing the high to short to ground when you turn it on? You'd only see that when you turned on the high beam too.