[mattsz]

Yeah, looks like it was mounted too close to the headlight.  Bummer. 

There's no place else to put all these cables.  2-1/2 years with no melting...

[sparklow]

The first time I took the headlight off on my B5 and noticed the individual push on connections for the headlamp I made note of the connection sequence, cut the push connectors off, and soldered on a standard molded headlight connector using heat shrink tubing over all splices. The RE method of push on connectors is not adequate in my experience while the molded one piece connector can handle heat in a much more satisfactory way. I am not saying that this was your only problem but it may well have contributed to this failure.

[caricabasso]

The contacts Headlight Lamp are very precarious and space is very limited.
This causes a contact with the speedometer cable and the positive  goes to ground, creating a lot of heat.
I have completely redone the wiring of the lamp for just this reason.
Your cables are rusted precocemenet because of the heat that has developed from contact with the positive lead of the lamp.
The new models have the ring of light longer and therefore more distant from the speedometer cable.

[longstrokeclassic]

Unfortunately caricabasso has hit the nail squarely on the head. The short  has generated enough heat to liquefy the plastic lining inside the throttle cable which has solidified around the inner cable seizeing it solid. The discolouration on the blue feed wire insulator sheath identifies this as the source of the short. It has been dislodged at some point leaving an exposed live wire when the main beam is on. Both of your throttle cables are dead centre right behind the headlamp bulb. The speedo cable situated behind them picked up a little heat off the throttle cable at the same time.

[singhg5]

The contacts Headlight Lamp are very precarious and space is very limited.
This causes a contact with the speedometer cable and ilpositivo goes to ground, creating a lot of heat.
I have completely redone the wiring of the lamp for just this reason.
Your cables are rusted precocemenet because of the heat that has developed from contact with the positive lead of the lamp.
The new models have the ring of light longer and therefore more distant from the speedometer cable.

+1 - Perfect explanation of what may have really happened.

@ Mattsz:

Your nacelle looks cleaner than my G5, which has lots of wires all over. But in my G5 the throttle cables are WAY BACK in the nacelle, farther away from headlamp connectors than your B5. There are wires in front of throttle cables that block their contact to the back side of headlamp.

Just curious to know if you had re-routed the throttle cables at some point or brought them in front of speedometer cable ? Or you just moved them to take good picture ?

[JVS]

Are both the headlight filaments operating properly?

[mattsz]

Thanks guys!  Just to keep the discussion going...

The contacts Headlight Lamp are very precarious and space is very limited.
This causes a contact with the speedometer cable and the positive  goes to ground, creating a lot of heat.
I have completely redone the wiring of the lamp for just this reason.
Your cables are rusted precocemenet because of the heat that has developed from contact with the positive lead of the lamp.
The new models have the ring of light longer and therefore more distant from the speedometer cable.

I'm not quite sure why a live wire would short electrically against a plastic cable covering, but obviously something happened.  My photo of the headlight isn't at a good angle to show the three wires in relation to each other... they're straight and not able to touch each other, anyway.  You can see how the wires are bent sharply just next to the connectors, though, which suggests they're wedged tightly against other bits in the nacelle.  They've looked just like this from day 1.  Do you happen to have a photo of what you did to re-wire your light?  I see another visit to my local auto-parts store in my near future...

Unfortunately caricabasso has hit the nail squarely on the head. The short  has generated enough heat to liquefy the plastic lining inside the throttle cable which has solidified around the inner cable seizeing it solid. The discolouration on the blue feed wire insulator sheath identifies this as the source of the short. It has been dislodged at some point leaving an exposed live wire when the main beam is on. Both of your throttle cables are dead centre right behind the headlamp bulb. The speedo cable situated behind them picked up a little heat off the throttle cable at the same time.

If this is what happened, then it could explain why the cable is seized.  Still, it takes more than an exposed wire to make a short and create heat.  The wire has to touch something conductive to ground, and I wouldn't have guessed that a plastic cable housing would do the trick.  Unless the housing was already damaged and the metal coil inside was exposed to the headlight wire - and I just never noticed it - and the short was just bad enough to cause heat in that location, but not blow a fuse.  Makes me question the wiring and the effectiveness of the fuses - this could have set my bike on fire!

+1 - Perfect explanation of what may have really happened.

@ Mattsz:

Your nacelle looks cleaner than my G5, which has lots of wires all over. But in my G5 the throttle cables are WAY BACK in the nacelle, farther away from headlamp connectors than your B5. There are wires in front of throttle cables that block their contact to the back side of headlamp.

Just curious to know if you had re-routed the throttle cables at some point or brought them in front of speedometer cable ? Or you just moved them to take good picture ?

Singh, maybe this is an argument in favor of the spider's nest ()?  With all the loose wires, it's easier to move them around and get them out of the way of the headlight?  With everything "cleaned up" and bunched together like on the newer bikes, it's hard to make room if you need some.  Those rubber shrouds, especially the one on the right in my photos, make it very difficult to access those connectors - there's very little play in any of the wires there.

The layout of everything in the second pic of my post above is exactly how it came from the factory (the third pic was taken while I was removing the cables).  I've had the speedo out before, but I left the speedo cable in place, and I was very careful to make sure everything remained as exactly like the original as I could, assuming it was the best way.  Maybe the 7" headlight protrudes further into the nacelle than the OEM smaller light?  Anyway, I will definitely look at re-routing the new throttle cables!

Are both the headlight filaments operating properly?

Yes, they were.  No obvious signs of trouble.  Both lights worked properly, I noticed no funny smells or smoke while the bike warmed up, the battery has remained charged well...

[JVS]

If it was a short you would have either blown a fuse, blown either of the filaments, or your HL would act in a funny way with any leakage current.

It is either that the heat has stuffed it up due to poor quality of the plastic. Or, your throttle cables were in a tight arrangement and whenever you turned the handlebar, the cable has rubbed on to the head stem/frame tube repeatedly; leading to the plastic deteriorating. It doesn't take much for that to happen. If you see scuff/abrasions on the inner side of the frame tube as seen in Pic 1 of reply #5; then you can conclude whether the 'rubbing' was the cause or not.

When you had lubed the cables a month ago, did you do any other work on the bike that might've indirectly or directly lead to the throttle cables being moved around or adjusted?

[mattsz]

If it was a short you would have either blown a fuse, blown either of the filaments, or your HL would act in a funny way with any leakage current.

It is either that the heat has stuffed it up due to poor quality of the plastic. Or, your throttle cables were in a tight arrangement and whenever you turned the handlebar, the cable has rubbed on to the head stem/frame tube repeatedly; leading to the plastic deteriorating. It doesn't take much for that to happen. If you see scuff/abrasions on the inner side of the frame tube as seen in Pic 1 of reply #5; then you can conclude whether the 'rubbing' was the cause or not.

When you had lubed the cables a month ago, did you do any other work on the bike that might've indirectly or directly lead to the throttle cables being moved around or adjusted?

Leakage current: I always look to see that my headlight is on, but I've only ridden in daylight recently, so the light could have been dimmer than usual and I might not have noticed.

The throttle cables have not been rubbing the head tube.  They're held away from it by the thickness of the speedo cable, which is held away by the brake line.  You can see the speedo cable housing damage, too, but it looks melted from contact with the hot throttle cable housing, and not worn by being chafed over time.

By this reasoning, it's the brake line that should be rubbing against the head tube - I wonder how it looks?  Something has to contact the head tube - I wonder... I've seen in woodworking catalogs, thin adhesive-backed "teflon" (or some other slippery compound) tape being sold to stick on your table-saw or what-have-you so that wood and other fixtures will slide easily.  Something like that on the head tube (or around the cable housings) to help protect whatever is rubbing there?  (example: http://www.leevalley.com/en/Wood/page.aspx?p=32182&cat=3,43576,53293&ap=1

I did pull the headlight to fix the intermittent neutral light, but I didn't mess with the cables - all I did was find one of the connector plugs (on the right in my photo) had worked loose.  I plugged it back in, and closed everything back up.  I noticed no melting or rust at that time - not to say it wasn't there, though, and I could have caused a problem when I reinstalled the headlight.

[ace.cafe]

Similar things like this have been happening ever since there have been Bullets.
The wiring in the headlight casquette is always rubbing on something or other, and insulation gets rubbed off, or things get moved when turning the handlebars, and eventually something happens. It's not always electrical, and sometimes cables get pinched, or whatever.
In the older Bullets, it is the connections at the ammeter that are always getting shorted out or touching something.

[mattsz]

In the grand scheme of things, this isn't really that big a deal, I guess.  Like I said, there was no fire, my throttle didn't stick open while approaching a busy intersection, etc...

I am thinking more about chafing gear in there, though. (I was going to make a comment about baggywrinkle here, but then I googled it and found the "urban dictionary" definition, so just forget it.  Kids are ruining everything!  )

[caricabasso]

The contacts of the headlight lamp compress the speedometer cable and, after a while 'time, cut the plastic coating and go to mass on the spiral iron sheath odometer cable producing heat and melting much of the plastic coating.
In practice the spiral of iron of the odometer cable in contact with the positive pole functions as a resistor and heats up.
Do not forget that the lamp has a power consumption of 70 watts and therefore the heat that develops in the case of mass is remarkable.
The fuse in this case is not stressed and the lamp continues to work with the exception of the dipped beam,
If you remove the lighthouse you will see a sign on the cable jacket odometer procured their contacts headlight lamp

[gremlin]

.........I was going to make a comment about baggywrinkle here, but then I googled it and found the "urban dictionary" definition, so just forget it.  Kids are ruining everything!  )

I dunno, that barley wine ale looked pretty good to me !

[mattsz]

Anybody know of a NAPA part number for a single headlight connector I could get to rewire this headlight?

[GSS]

Any auto place will have a H4 or 9003 socket.

http://m.napaonline.com/Tablet/parts/PartDetails.aspx?Id=NW_787108_0495955483