I have a strange problem with 400ex. If my headlight is on when I start the bike, about 5-10 seconds later it blows the fuse. Also every once in a while during riding it will also happen but it consistently happens during ignition and after it blows a fuse if I replace it, start it, and then turn headlights on it happens again. Any ideas on how to diagnose it?

 

you've got a short someplace... unfortunately electrical problems are no fun to mess with...

first i would hook a volt meter up to the system. w/ it off you should be seeing 11 to 12.5 volts roughly.. with it on it should be 12 to 14.

its possible that the bike is getting too much voltage so when its running its overcharging the system....

what about the tailight any issue w/ it?

after that disconnect the lights and make sure the bike runs like it should and make sure you are seeing the correct voltage.

it that all checks out check all of the wiring for the headlights you have have exposed wire that is grounding out....

hope this helps..

 

Found the short... wire gets cut by the headlight lamp housing then shorts out, guess this is quite common. Taped it for now and ordered a new headlight socket for $13. Thanks for advice