2003 wr450f headlight problems

I have a 03 wr450f and my headlight is super dim when idling (can't even see past front fender) and as soon as i start going the light seems fine for a couple of seconds then the bulb blows i changed the rectifier/ regulator same thing is still happening can someone help me out please

You will need to measure your voltage at the headlight terminal. was it a new or used reg? could be the stator I suppose, are you sure you had the right bulb? the light circut is AC not DC. Not sure if that would make a difference or not....

I don't have a service book for the bike and every where i look wont give me an answer for the voltage on the headlight terminal. the rectifier is brand new yamaha oem. And i don't think it's the stator because my battery is holding a charge perfectly fine. And yes i have the right bulb.

WR450s have two essentially separate electrical circuits. There are two poles off the stator. One of them goes to the regulator/rectifier, producing DC to the battery, starter, and CDI. The other goes to the lighting, and the regulator only side of the r/r. The regulator side is in parallel with the lighting. I'm guessing a bad ground on the r/r could lead to excessive voltage on the AC side. 

 

I managed to find a manual in perfect shape for $11 shipped off ebay. It's for an 04 rather than an 03 but there aren't many differences. I don't see any that cheap right now but keep your eyes open and pick one up when you see one. http://lolinter.net/wr450/wr450diagram.pdfis the wiring diagram, http://lolinter.net/wr450/WR450.pdf is a manual but it's trilingual and in my opinion not as good as the paper one. Good luck. 

Edited by toten

Okay I'll check that out thanks i appreciate the help

13-14v AC at the headlight is what my manual says. Lighting coil resistance should be 0.224-0.336 ohms

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