Grey Gray wire mod misnomer?

I have a 2000 WR400FM, looking through all of the archives here, thumperfaq, motoman393, etc. all refer to the free mod that changes the ignition map from WR to YZ spec as the "grey wire mod".......

Here's the thing, I'm in my garage right now, with my service manual, sitting on the bike, tank off, CDI wiring harness in front of me, and there's only ONE Gray wire in the entire schematic, and it's part of the kill switch, not part of either of the 6 pin connectors, as described in other threads, the other 6 pin connectors have wires labeled as P, Br, W, B, G, R and O, B, Sb, L, Y, B/L (The color code indicates that the G = Green)

I read on here the tech. analysis of the CDI unit from a WR250F that the gray wire was a ground, that "told" the CDI to work from the WR map, and when not grounded, it'd work off the YZ map.

Now, again referring to the Yamaha factory service manual schematic, the only wire that's connected to ground in any way, off either wiring harness are the wires labeled B = Black......

So thumpertalk gurus, which wire is it????

I've got an 05 Wr 450. I have run with the grey connected and disconnected just moments apart. I can't see any different performance. I left it connected and had a beer and forgot about the whole thing.


Congratulations on your '05 WR, your forgetfullness, your alcoholism, your lack of reading comprehension skills, and your performance guage buttocks.......

anyone (else) want to give a shot at the query? What I'd like to know, is which wire, if not the gray wire as part of the kill switch circut, is the wire to cut?

It seems that just like most other forums, normally, if you ask a simple question, you get either "use the search feature" or a link, but most of the referrals that I've found searching "gray grey wire mod wr 400" gets you over to, which is close, but it's a different bike, different wiring harness, different colors on the wires. I've learned alot using the search function, found most of what I was looking for and even some good tid-bits that I wasn't looking for.....

But the gray wire mod specifics have escaped me thus far......

OP- Good question--which wire is it?

Only speaking for searching on my 99', I cant find any real evidence that anyone has actually done it or documented it for this model year. My guess it doesn't exist for 99and even some 2000's. It seems only on later models. Is it possible reasoning that the factory had a WR CDI and a YZ CDI in early production years, and to to save money,-later made a switchable CDI via the grey wire mod.....Just speculation for what it's worth..

If I remember correctly on your vintage bike the gray wire mod doesn't apply. I beleive it came about on the '01 WR's . Your bike used the de-ocotpus mod, the BK mod and possibly the YZ timing mod, which by the way was the best bang for the buck on my old WR426 and my perceptual butt dyno. Good Luck

WR Dave

Disregard!!!! This is the Nuetral Switch mod...I pledge to research before I post again...Sorry I was of no assistance.

I cannot confirm this, but at one time I thought I'd read that the light blue wire from the CDI to the connector was the "ground", and removing that had similar effect as the grey wire. This was specific to the WR400.

Again, this is a recall of previously read information, and hopefully relevant to your search.

Edited by 2in2out
Poster had head up A**

I thought that I read somewhere the the gray wire mod went hand in hand with the throttle stop mod. Unless you shortened the throttle stop, the gray wire mod really wouldn't buy you anything.

The light blue wire is the neutral detect circuit. It supposedly produces a hotter spark, or something else that makes starting easier with the wire removed. I honestly don't remember what it did exactly. What I DO remember is that when I removed my light blue wire the bike started much easier and required a little less leg. I even started the bike in a pair of Birkenstock sandals (not smart I know, and haven't since) to see if it was just a placebo effect.

Grey wire alters the timing of the CDI cleaning up the midrange on the WRs. The mod and the throttle stop do not correlate directly. Of course, if you can't open the throttle you cant get the RPMs up to where the grey wire comes into play so I guess its a quasi-correlation. The throttle stop is purely a physical limiter for how far the carb opens. The grey wire supposedly was there purely for EPA emissions purposes. The YZ did not need to comply with EPA as it is technically a closed-course only bike.

I am trying to do this on my relic ('98). So is it the light blue wire?

Resurrecting this because I have a 98 WR400f and can't find any specifics on this mod. Can anyone clear this up, possibly with pics?

Go to the main harness junction behind the left side plate

Pull the harness apart.

If you have a gray to gray wire in the harness, you push it out on one side of the molex, and tape it off, or re-position it into an unused opening

It changes your TPS mapping changes about 5 degrees advanced.


Tons and tons and tons of info if you do a search.

What do you mean by "side plate?" There is information out there but it is very conflicting.

What do you mean by "side plate?" There is information out there but it is very conflicting.


No, it isn't really.


All models, all years, have their harness in the exact same place

You're saying it's on the left side, in the FAQ it says it's on the right?

Do some searching around. There cannot be too many grey wires that if you disconnect the bike will run.

Utube WR250 grey wire mod

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