I have a 2003 grizzly 660 and I have weak charge @ battery @ 13.25v and when I turn on headlights that are factory it falls to just battery voltage 12.47v I think it's the rectifier and have checked the red wires for corrosion and stater seems to ohm good on all three legs

 

Could be the voltage rectifier, amazon one and if it does not work , send it back.

 

Charge the battery up fully and have it load tested first. If it's up to snuff and only shows a little over 12 volts with the idle up and lights on then most likely it's a regulator.

 

Ya I charged battery and it load tested good so I installed new rectifier and brung my voltage up to 14.2 @ idle but would still fall a little to 13v with factory head lightsand with led lights on at same time 12.87v @ high idle, stator ohm good on all three legs, thanks for the info