Yamaha WR 250 2003, lights get brighter when you rev it and blow after a few seconds. Is there a regulator to control this

Dose the headlight get quite a bit brighter when you rev machine up, if it does it probably is still a regulator issue. You could see about installing a in line resistor if there is not one already or see if you can pick up a heavier bulb.

Wiring looms for these are cheap enough on ebay, i suggest buying one and replace the lot, also check your fuses.

Voltage regulator has failed.

well, its not the "circut breaker" aka the fusebox, so there has to be a problem with the regulator. when you say headlight "blows" do you mean the actual bulb burns out, the fuse burns out, or the light just turns off? it matters. on a side note, if your headlight stops working, its normal for all the other lights to get a little brighter due to the extra power for the headlight going to the others.

you will know if the regulator/rectifier goes, if 1, all your lights go much brighter and blow when you rev the bike, or 2, if your battery is not charging. a simple test is to check the voltage at the battery with engine idling, should be about 14volts. There is nothing you can do to prevent the rectifier from going.

it sounds like there is toooo much current going through your system, check how much voltage comes to the indicator when you rev it up with the multimeter if more than 13.5v check regulator

check the wiring, make sure that you are using the bulb with the correct rating. Also get the output in the headlight connector checked.

Lights going brighter on reving generally means the battery is getting weak. Check the water in the battery. There should be enough to cover the top of the plates. When the engine revs the flywheel generates more electricity. The battery buffers the power. A weak battery does not buffer the extra power very well.

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Unhook exhaust pipe,check port for blockage. if it is clear try to rev up with pipe off.If exhust is clear you will need to check high side of carb. good luck