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Hey, my 08 400ex headlight recently went out, meaning both of them at the same time and I don't think its the headlights them selves, and other than that I have no idea, and I cant find anyone else with the same issue, they started to flicker a little and they flickered a few times more then poof, both of them went out at the same exact time, that's all I know and was wondering if someone can direct me to a possible blown fuse or loose ground and tell me where that could be because I cant find it for the life of me.
 

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Check the bulbs first - if the bulbs are good, then you either had a loss of power or a loss of ground - there is no fuse in the headlight circuit.

If the bulbs are bad, there's a good chance the voltage rectifier/regulator failed and a high voltage surge burned out the lights. Check the voltage across the battery terminals with the engine running at about 2000 RPM - should be no higher than 14.8 volts DC - if higher than 14.8 volts, test or replace the rec/reg. A bad ground on the rec/reg could cause the same problem without the rec/reg being bad.

Check the ground by checking continuity from the shell of the light to the engine - if you have continuity then check for a loss of power - if no continuity, check the motor mount bolts to make sure they are tight.

Checking for power is a little more complicated, but still pretty simple - first check for 12 volts on either the blue or white wire at the head light (high is blue and low is white) - if you have power at the bulb socket, recheck ground - run a wire from the bulb socket to the neg terminal on the battery, if the bulb lights, touch the wire to a motor mount bolt, if the bulb lights, touch the wire to the motor - if the light lights in all instances, you probably have a defective wire inside the wiring harness. When the key is turned on, the red wire is connected to the black wire - if any lights or the electric starter work, that connection is made - the black wire connects to the brown wire at the handlebar switch, if the tail light is on, the brown wire has power - the brown wire connects to the headlight via the dimmer switch - if the taillight has power but the headlight has no power, the dimmer switch is probably defective.
 
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