Where is it? my book dosn't tell me..I'd like to change it, I eat light bulbs....

 

You might want to check the voltage at the bulbs using a multi-meter. Atv's can eat bulbs from all the vibration just from riding.

 

Most quads limit out at about 15. volts, so if you connect a voltmeter across the battery terminals, and rev it up, it shouldnt excede 15.5 or 15. volts.
What model and year is it?

 

Battery?[img]i/expressions/face-icon-small-disgusted.gif[/img] Found it, changed it..I'm pretty sure it wasn't from Vibration, the bulbs would last until it got some good revs..

FWIW - it's on the right upper frame-rail, under the tank...

 

Im not sure what thats all about.
But this is how the voltage regulator is checked. You put the voltmeter across the battery and run it up to 4000 rpm and watch the voltage. If the regulater is responsible for burning up the filaments of the bulbs, youd see it in the voltage reading, If the volts dont go over 15 volts...then the regulator isnt the problem. And usually if high volts ate the bulbs, then the inside of the bulb will look all gassy and have a metalic sheen. If the filiments just break from vibration , then the bulb glass is clear.
Im just trying to save you some money...instead of tossing parts at it. This is how to troubleshoot the problem, and its definitive.
Sorry if i offended you.