Orphan yellow wire

[fredintoon]

Hi List,
the tach on my XS11SG started acting up.
Every now & again it would quit for a while and then start up again. So I start looking for a loose connection. I found it where the wires from the stator plug into the main harness. The connector is half-melted and the terminals are kinda burnt looking, that plug is toast. I'd have to remove the sidecar to do a proper fix so I connected each white wire with a bullet connector pair. But here's the weird thing. There's 4 wires coming from the stator, 3 whites and one yellow and they go into a 4-way plug. The housing from the main harness matches the plug but there's only 3 connectors in it and there's only 3 white wires lead out of it into the main harness.
However, the fix works, the tach works full time now.
So WTF did that yellow wire do, seeing that it never did connect to anything?

[3Phase]

I believe it's a center-tap for the wye-wound 3phase stator.

1978 and 1979 XS11s use that yellow wire to run the headlight relay.

From 1980 onward the yellow wire was omitted and a diode was attached to one of the stator wires ahead of the regulator/rectifier to provide DC for the headlight relay. The yellow wire was still run out to the main wiring harness connector but left unconnected past that point.


Regards,

Scott

[fredintoon]

Typical Yamaha

Hi Scott,
yeah, I knew the yellow wire operated the safety relay on the XS650 which also turned the headlight on. And as you say, it used to turn the headlight on earlier XS11s. Doubtless, just like all XS650's have 3 valve covers with 3 M6 fasteners and one with 4 M8s because they gave up on the compression release after one year but still had a warehouse full of head castings; They must also have had a warehouse full of XS11 stators with the yellow wire in them.

[3Phase]

Hello, Fred, I did not know that XS650s had a compression release. Thank you, I learned something!

As a general rule - never assume and always test first! a 4-wire winding is wye and a 3-wire winding is delta. What Yamaha did with the neutral tap is a hack. It works so it's not dumb, but it's still a hack.

Here is a simple automotive alternator PDF covering the basic types of windings, wye and delta.

An automotive alternator can safely 'float' the neutral tap because the relatively low voltages and currents involved are mostly safe for humans and because it is less expensive to do so.

Usually when a neutral tap is connected to ground it's with a rather large and solid connection. That's so you can plug in Mr. Coffee without the Presto HotDogger effect from a neutral that's floating several hundred volts and thousands of amps above or below -- whoa! earthquake!!!!1 111

Okay, that was fun... a tiny little 5.8 earthquake 29 mile ESE of Los Angeles.

Aaaanyway, moving right along, what Yamaha did with the yellow wire is ground the neutral tap through the headlight relay.

That is okay while the stator coils and their loads are equal. When they are not equal because of bad connections, bad windings, a bad rectifier, etc., then current flows in the neutral. It's not particularly dangerous but eventually the fine wire in the headlight relay holding coil becomes a fusable link and the alternator goes back to a full-floating wye.


Regards,

Scott

[fredintoon]

I did not know that XS650s had a compression release. Thank you, I learned something

Hi Scott,
XS650s only had a compression release for one or two years, right after they started fitting the bike with an electric starter. The release lever looked like a half-size clutch lever on the handlebar. You pulled it in to operate a cable that partially opened the left exhaust valve. The lever also operated a switch to run the electric starter. The manual lifter was built into a left exhaust cover which was made square instead of triangular and was held on by four M8 studs rather than the three M6 studs that held the rest of the covers on.
After they worked out that the lifter was not necessary they discontinued fitting it but (I presume) didn't want to pay for new cylinder head dies so kept cranking them out with one odd valve cover.

[3Phase]

Re: Thank you, I learned something!

Originally posted by fredintoon
Hi Scott, XS650s only had a compression release for one or two years, right after they started fitting the bike with an electric starter. The release lever looked like a half-size clutch lever on the handlebar. You pulled it in to operate a cable that partially opened the left exhaust valve. The lever also operated a switch to run the electric starter. The manual lifter was built into a left exhaust cover which was made square instead of triangular and was held on by four M8 studs rather than the three M6 studs that held the rest of the covers on.

That is a neat solution. I wish I had electric start on the compression release on my first motorcycle.



It was a '64 Bultaco 175. Man, I loved that bike: Brit controls and a 4-speed gearbox; dual spark plugs and coils with a compression release that I definitely needed. At 13 years old and maybe 110 pounds that 'Sweet Old Bike' would launch me without breaking a sweat, but once it started the engine had throttle response like an electric motor. It was fun re-learning the controls and reflexes for more conventional bikes.

After they worked out that the lifter was not necessary they discontinued fitting it but (I presume) didn't want to pay for new cylinder head dies so kept cranking them out with one odd valve cover.

I've seen more than a few items that were dropped by factories that retained vestigial traces of the old designs until someone got the 'round tuit and a budget to change the production line before the old stock ran out.

Who knows what Yamaha was doing but I don't believe they wound their own stators. To me, bringing all of the stator connections out to one connector says, "Manufacturing test jig."


Regards,

Scott