Could a WR450F electrical system "burn out" in a way the bike still runs?

Hi all,

I have an '03 WR450F that went in for a new top end... when I left it at the mechanics the battery was marginal at best... and after sitting almost a year while the bike got fixed (don't ask)... it was totally dead. I could still kick-start fine.. bike ran like a top... but e-start was _dead_... and I had other symptoms like the bike would blow headlight bulbs in a couple of minutes (another post I made here).

So I bought a new aftermarket battery... trickle-charged it to top it off... then ran it on a weekend DS trip. Bike started fine: e-start always lit it up right away all weekend... but I wasn't really using any battery power (i.e. headlight was shut off). Though I did test the headlight for about 20 minutes into the first ride to make sure it wasn't eating bulbs any more.

Bike sat one week. Then I had to ride about 2 hours in the early morning, headlight on, doing 50-80km/h... to where we were going to ride that day. Headlight worked fine... but after stopping after the ride in the e-start wouldn't work: just a rapid clicking sound when you stabbed the button. Also, perhaps related, I had put on a new pipe during that week when the bike was parked (didn't touch the electrical system: just 2 bolts to put on the new pipe)... and during about the first 30 minutes of the new ride when I stopped I could smell a faint burning smell. I thought it was just the packing in the new pipe heating up for the first time. Maybe not?

Anyways, by the end of the day the bike showed symptoms of a really dead battery: even the _LED_ turn signals refused to come on some time... and the electronic flasher didn't even "flash" them anymore. Also... normally at the end of the day I'd air up my tires using one of those small Slime air compressors. Normally I'd leave the bike running while the compressor was on (didn't have to, but wanted to keep the battery fresh). This time the compressor wouldn't run at all when plugged directly into the battery... and when I started the bike up (kickstart) it would _stall_ the second I flicked the compressor on. Limped to a gas station to get some air instead...

So, I know that's a long story: but the bike still kickstarts fine. Is it possible the electrical system is "broken" in a way it can still keep the bike running (i.e. enough power for a spark) but not be able to keep the battery topped off?

Also, I went out and bought a new OEM (Yuasa) battery: exact same model Yamaha shipped the bike with. Gave it a full trickle charge to top it off. Put it in the bike... hit the e-start: rapid clicking again and the bike didn't turn over. Crap!

I have a manual and multimeter: so I can get a start on diagnosing the problem myself. I'm just hoping some of these symptoms sound familiar and someone will point me towards whatever little electronic gadget may be dead.



i would say check the rectifier regulator. if u jump the starter relay with the new battery will it crank over?

Stock WRs have stators have two windings; one to charge the battery and one for the electrical. The lighting system is AC and the battery charging system is DC. Under normal circumstances it doesn't take much to charge the battery because it's only used for starting.

Since you have LED turn signals and a flasher, and you run an aircompressor your system is obviously modified. You need to get a WR manual if you don't have one and start with checking the wiring diagram to your bike to see what's different.

Back to the first paragraph, if your stator has not been modified for the extra load of the add ons it won't be able to keep up.

I've got a dual sport 04 WR450F that had something similar happen. There is plenty of power in your battery and electrical system for everything, but it has to wired correctly. The stator puts out AC voltage for the lights, (Yellow wire), and separate AC for charging the battery (White wire) which is then put through a rectifier to convert the power to DC, then it is put through a regulator so the voltage won't go too high, (the rectifier and regulator are both in one unit), then it is passed to the battery to keep it charged. Mine had the headlight connected to the battery, and the battery would keep going dead. I suspect the headlight was using up the battery faster than the bike could charge the battery. I put the headlight and tail light back on the Lighting AC side where it was from the factory, (Yellow wire), and all is good now. The horn and signals need DC, so keep these on the DC (battery) circuit. They are not used much, so won't draw down the battery.

sorry for th thread hi jack but my 05 450f has some assostiated issues to this, if my bike is idling and i switch on the indicators, they dont flash but if i bring hte revs up they will flash, also my headlight gets brighter, is something on the way out or is this normal, i dont really car as i dont use the indicators much but just curious.


fully charge the battery with your trickle charger, start the bike with kickstarter, check the voltage at the battery, should be around 14volts dc, if its under 12.5 then you are not charging the battery, could be either your voltage regulator/rectifier or stator. Then unplug your head light there should be a yellow and black wire, put your meter on those 2 wires y should be positive and b should be negative, turn your lights on, this circuit is ac voltage so you need to adjust your meter, you should have around 10 vac. rev bike up slightly, voltage should stay relatively constant, if it goes up around 20 vac then your voltage regulator/rectifier is shot, if you have no voltage then your stator is done for. Hopefully this helps

aussieklx: I had the signal problem too. The light bulbs were not drawing enough current to make the flasher work. I replaced the bulbs with brighter (higher wattage) bulbs and it worked great.

doctorchopper : I think you may be on to it. A bad Rectifier/Regulator was probably blowing the headlights. Someone probably rewired the lights to the DC side so they would not blow, but that caused another problem and did not fix the reg/rec problem.

Do the charge coil and lighting coil tests in the manual. They will tell a story.

The Baja Designs stator mod verifies that the battery will not run the lights without draining the battery, but that mod is not necessary. I have an 03wr250f and an 04 wr450f that I dual sported myself, and they both work good. The secret is that the headlight and tail light must be wired to the AC lighting coil (Yellow wire) as they were from the factory. Wire the horn to the DC battery side (Brown wire). The BRAKE light can go on either. Signals can go on either unless they are LED or have an electronic flasher, then they need DC. Just make sure you do not put anything on the DC side that is constantly drawing power.

the rapid grrrrrrrrrrr from under the seat is usually a bad starter relay, not affected by battery voltage

i am also plated and only time my battery goes dead is when i leave the ign. switch on

i use the drc kit from

and run a langston racing headlight

I did eventually fix this.

I tried a new starter relay, and that wasn't the problem. Then I checked the AC voltage running to the headlight when the bike was revved... which pointed to the rectifier/regulator being bad. Swapped that out and I was almost back in business... because I had gone on a couple rides with the old setup and the new Yuasa battery... which apparently permanently damaged the battery.

So, put in yet another battery... went for a test drive... now I'm no longer blowing headlights... and the bike still cranks over fine at the end of the ride (hopefully meaning the new rec/reg isn't eating this 3rd battery).

The first suggestion in this post was the right one... if I hadn't convinced myself it was a stator or relay problem... and just hooked up a multimeter to the headlight as my first test... I would have saved myself about $150 in battery, new relay, and a handful of headlights.

Live and learn I guess :banghead:

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