1988 Yamaha FZR400. The problem:

The headlights both died about a month ago at some point (noticed it later at night). The engine started normally, and all systems go including the taillights and both sets of blinkers. After some examination, determined one of the fuses was blown. Fuse was replaced, headlights came back on.

Now, the exact same thing has happened again, but all fuses are intact and I have no idea was else to do besides checking all of the wiring. I'd really rather not do that because it was mean cutting the covers off to do it.

Any other ideas?

 

I would determine the wattage of the bulb you have in the bike and see if the owners manual recommends the same wattage. Or check that the fuse is the propper one for your lights.

 

check the base for proper fitment, and TIGHT clip retention.gotta make sure the female 1/4" plugs are tight on the teminals of the bulbs.if they loosen up they'll arc over. this will A. blown your fuse. B. pit and corrode the bulb terminalsand socket (base).

make sure you got 12V at the socket and just work back.. i always tackle electrical stuff on low voltage systems from the load, back. no power at the bulb?.. go to the next termination point, whether that be a relay, or the h/l beam selector switch, no power still? go back to the next termination point, and so on.. once you get 12V.. isolate and repair the connection or device impeding current flow.. sadly this troubleshooting will require fairing removal, which i know you're trying to avoid..

triple check and make sure the fuse is good. never look at it and assume.. the break can be soo fine you can't notice it.. it'll look good, but will not pass current.

fuses are very sensitive, bro. on an AC circuit, they will blow in 1/4 of a sine wave. that FAST. theres 60 sines in one second. circuit breakers, on the other hand, will take sometimes 125-200% of the rated load before tripping.. so you can always plug in a self-resetting breaker to track down the trouble spot.. it'll give you just enough power for a bit to track the fault..

DC actually provides WAY more power than AC does, so a fuse will pop (or a breaker) way faster.. the voltage never drops to 0V like in an AC system.. you can actually use a compass to find electrical faults as well.. old skool trick.. the needle will point to the energized wire all the way up to the point where the current is stopped.. i.e. a break in the wire, faulty relay or switch, short.. ect.

oh.. make sure (i think, anyway) that when you test, you start the bike up first, then just hit the kill switch.. i know alot of bikes don't turn the headlights on with the key.. motors gotta spin, first! yours may be different?

good luck man!

 

wow, that is pretty deep wh. Need to try that compass thing out sometime

 

electrical engineering degrees pay off every once in a while..lol

yup. the compass trick is wicked . no matter what voltage is present, or what type of power it is, a conductor will ALWAYS have a magnetic field around it. the needle point to the wire the whole time under load, up until the load is removed, power is removed, or the power is shorted. in which case, the needle will point to where the short is. (if its not blatenly obvious..)