Honda XL 250 Resource Site

Notes on Honda XL 250 Electrical System

This diagram doesn't include any indicators.

I recently found this diagram, it's in Japanese but it's interesting nevertheless.

I note the indicators are two wire ones. I think it might show what the strange red light on the Honda Collection Hall XL250K3 is for. Note the speedo is in KPH, no mention of MPH.


Anyone read Japanese?The light shown just behind the headlight seems connected to the the speedometer. Maybe the red light comes on if you hit a certain speed limit? See Peach on the Honda wiring colours below, it mentions speed warning light.Hmm..

So, later, I emailed the nice man in Japan from whose site I found the circuit below. This was his reply

"OK, Richard san.
That is Red lamp at a speed warning light, through the speed warning unit, and is connected to the sensor, which is built-in speedometer.
In Japan, the legal speed bike on the highway at 80km / h up to October 2000, I drew attention by lighting the red lamp it is more than 80km / h."

His website is


Now, there is a guide to Honda wiring colours HERE but it was translated from Japanese by Goggle and some bits are odd. Brown appears to be called Tea, pink is called Peach and under Green it's ducks and turnips? Under Blue there are Mighty Ducks! WTF! Enjoy!

Here is the K2 one in English.1976 K3 is much the same, except there is no 3.61 Ohm wire wound resistor and indicators are one wire, ground is made through frame.


The xl250 k series are 6v,  the generator is made by  Denso (headquartered in the city of Kariya, Aichi Prefecture, Japan. Established December 16, 1949 as Nippondenso Co. Ltd now known as Denso Corporation)  with output of a maximum of 80 watts at 5000  revs, and the AC (alternating current) generated is used as AC for the ignition but also transformed into DC (direct current) by a  silicon bridge rectifier mounted near the battery. This is item 6 in the schematic below.  
The generators have 3 generator coils  but look at the generator and you will only see  two, one is a bit bigger than the other, that's because it is  two, one wound on the other. 
Of the three real coils there are  also three separate functions;  the first is to start and run the bike  by providing ignition system power, the second runs the headlight, so it is said to be important to replace even the main beam indicator light on the headlight shell to present a full load to the coil and help stabilise the voltage, as the K3 doesn't have the 3.6 Ohm resistor that earlier models have. The third one charges the battery.

At 6 Volts, every 6 Watts is one amp so a 24 Watt bulb is going to need 4 Amps to run it.
At 12 Volts every 12 Watts  is one amp so a 24 Watt bulb is going to need only 2 Amps to run it. 

As the  generator/alternator  produces alternating current (AC), which light bulbs are happy to run on, like in your home, there is no need for this to be rectified into direct current (DC).
However the battery can only hold DC so the rectifier changes the AC to DC by a diode  network that is a rectifier. The battery  then powers the side lights, the horn and the indicators.  This is so that if your engine dies  say in the pitch dark of an unlit  crossroads, you are still visible to other road users and can still express your annoyance by sounding your horn. Its a safety thing.

Having a blown bulb is therefore a bad idea, The usual problem of blown bulbs is due to off road riding where the filaments get shaken till they break, or old age. It is noted that some apparent headlight bulb failure is mainly attributable to poor quality Chinese bulbs, rather than an electrical problem.

As tungsten filaments age they deposit a layer on the inside of the glass, which can look black or silver, but this not only makes the bulb dimmer but also  traps infra red (heat) inside the bulb which them runs too hot so shortens the life further. Any bulb with this effect apparent should be thrown away and replaced with a nice new shiny one. It is possible to regulate the voltage with a silicon voltage regulator, with a little ingenuity,  but it isn't fitted by Honda.

This means that the bike does not need a battery to start. However, it also means that there is an easy way to steal one as the ignition switch and the kill switch both turn off the engine by grounding (sending to earth = short circuiting) the ignition. Therefore if the ground wire from the ignition switch is cut, even with no key the bike will start,
so best to  lock it up.  The act of kicking the kickstarter turns the engine and the generator to produce enough voltage to energise the coil, so a good kick is preferred. 
My favoured method of starting is to turn on the fuel (down is main, up is reserve), check kill switch is in 'off' position, check ignition is 'on' and choke on full. Then a hard kick (or 2) with NO THROTTLE TWIST and the engine starts.
I push the choke in full most days  as soon as I am moving as it otherwise runs too rich and the plug can soot up. Note the engine doesn't have to be in neutral, as long as you pull in the clutch the kickstarter will work;  handy if you stall it.

The output of the generator means that it is  unwise to fit substantially bigger wattage headlight bulbs, they won't be much  brighter. 

The standard are 35W/35W (Bosch type base) you can buy 25/25  and even 45/40. Indicator bulbs are 18W and the stop/tail are 5/21.The neutral lamp is 3W and the dial  illumination and turn signal lights on the tacho/speedo as well as the high beam indicator  are all 1.7W
So, if everything is on, that's:-
35W main beam
5W   tail
21W brake
6.8W panel lights
36W  indicators

that's nearly 104 Watts plus ignition.  I appreciate we don't ride with indicators and brake light on constantly. Remember the alternator is 80W, and that doesn't leave  much left over.

Because the engine needs to be running to generate power for the headlight you only have side lights or parking lights if it isn't,   these being powered via  the battery. 
You can however  improve the headlight with a halogen version which is whiter/brighter, even though it is 'only'  a 25/25W. 
I use the standard lamp fitted by Honda San, but I keep a spare halogen one inside the headlight just in case  (they are smaller head than a regular tungsten one and take up less room in that crowded headlight).

I recently received an email from Michael C. which is interesting, which I should share with you, and reads like this:

"Hello Rich.

You have a lot of information on your site, and I owe you a few beers already for assistance in restoring a 1976 XL350 (American import).

Your suggestion on QH h/lamp bulbs may be off the mark.  The fluctuation in AC power that reaches the h/lamp apparently causes poor illumination very quickly, because the lower-than-working temperature of the filament causes the halogen gas to condense onto the glass and form a film that dims the bulb.

I'm planning to fit one anyway, though, after I rewire tho two side-by-side flywheel coils through the rectifier/regulator to the battery, and wire everything (but the ignition of course) in DC.

Keep well, and keep up the good work.

Michael C."
So it might not last as long.  The point really is bigger wattage is not the solution.

When I bought my bike  I found the front indicators had 12v instead of the correct 6v bulbs in, so that explained why they were dim. It is worth checking. 
There is a 10 amp (60 watts @ 6 volts) fuse in a little white tubular fuse case
(item 11 below) near the battery,  and a holder for 3 spare fuses inside the battery cover.
Since the generator output increases with engine speed, the headlight will be dimmer at tick over (1200 rpm) and get brighter with an increase in engine speed. This does however give a quick check to show the generator is working. 

If you look on the left side of the bike where the generator multipin block (white) joins to the loom you will see  an odd black unconnected short wire with a female bullet connector on it. 

Don't worry, you are not missing anything it is the access point to test the ignition part of the generator with a voltmeter, and is supposed to be normally unconnected. If the main wiring loom is removed, such as is often done on stripped down desert bikes, it is used to take power direct to the coil/points so the bike will run.

This is the one.

Part no. 5 above is very hard to find. 
Inside the headlight is where a lot of wiring connections are made and it can be a bit confusing because of the small space. 
I did a diagram to help me,  when I found the bike had a plastic headlight instead of the steel one (and no main beam light) and so I fitted a correct one that I happened to have. This was to get  clear what the handlebar switch wiring
from and to the headlight was. Maybe it will help you.
My diagram is below:

There is a good troubleshooting a spark article HERE courtesy of Dorkpunch on the AV Rider forum.

Incidentally, there is a good article from on timing bikes, see it HERE and there is a whole load of Dan's help HERE God Bless America.

Ignition coils and the XL250/350:

The ignition coil is part number 30530-376-405 and comprises of a coil with HT (high tension=lots of volts) cable out onto which a suppressor cap is fitted by winding the cap via a kind of self tapping screw built into the cap, onto the HT lead.

There is an LT (low tension=low volts ie. 6) cable that comes from the points via a japanese style bullet connector, and a condenser (a capacitor) to prevent the points arcing and burning out prematurely.

The coil is riveted (as is the condenser or capacitor) onto a bespoke steel holder that when new is passivated zinc plated in a yellow/gold colour.

The earth or ground is made to the frame via the body of the coil so the metal needs to be clean on the coil and the fame, and the mounting bolts tight. A bad earth/ground at this point will stop your bike running.

Now, the coils will age and after nearly 40 years they will have some breakdown in their internal insulation which comprises a thin coat of lacquer over copper cable that is quite fine and delicate.

There is no option if your spark is weak or non-existant but to replace the whole unit. However part 30530-376-405 is obsolete, (and 86 euros/US dollars from CMSL even if they had any which they don't) and rare to find NOS, and therefore the only choices seem to be to:-

1. fit another type of new coil (must be a 6V one) and condenser,

2. get one from a bike being broken for spares, but that will also be as old.

However, it occurs to me that since the actual coil bit (the black plastic encapsulated bit) is standard to many Hondas, why not just drill out the rivets and fit a new middle bit? Then I saw on ebay in Thailand this one:

compare to original one They are both AC6V models.

Basically the new one which is £21 free postage even unscrews (yippee), ie no rivets apart from the condenser, so if I drill out the rivets on the old and re-use the screws on the old one that I take from the new one and remount the new condenser, and the original cable retainer I should have a fantastic new coil that looks right and mounts right. The spacing of the two holes is a few millimetres different from the older XL250 ones, and the coil won't sit against the frame without the K3 coil frame.

I happen to have a spare coil that looks good but has a weak spark, so I'll do the swop on that one and tell you how it goes. The sun set, rose and set again, then I had a minute or two


So today the new coil came from Thailand, part number 30530-439-900 sealed in the original Honda box.

Side by side the original and new doner look like this:

First job was to remove the 2 largest rivets in my cosmetically good but 'weak spark' coil. The coils then just prises out.

Then moving to the new coil, Undo the two screws that are used instead of rivets, and put aside. We will need them later.

I decided to re-use the existing condenser since I have no reason to doubt it is OK. I will keep the new one in case I find I do need it.

The condenser wire is soldered to the coil, so it can be unsoldered. I broke the wire drilling out the left hand rivet, but I should have unsoldered it first shouldn't I?

The new 6v coil taken from the new assembly also needs to have the same wires unsoldered if re-using the original wires. Then solder the old wire onto the new coil. (actually it is two wires joined together, the green condenser wire and the black/white wire from the points) If you have a pot of the dip used in the article on the cramper somewhere else on this site, a blob of that on the solder join will dry as a nice durable watertight insulated cover to the join, like the original has.


The new coil, cable clamp and the bolts are used to fix the coil into the original K3 frame.

I used the new HT cable (which I snipped shorter) but the old plug cap for now, I notice the original HT lead has an extra cover layer on it, so I may swop them later.

Outcome, not bad for 15mins work on the kitchen table whilst the wife was out. I have no time to try it for a few days, but I will as soon as I can.

This is the finished coil ready to be fitted to my bike to test, with the discarded coil in the background. Beady eyed readers will spot an unused washer on the tablecloth, the bolt was just too short to use it on the condenser mount bolt, so I left it off.

Update a week or two later.

As the bike refused to start last night (luckily I was home) I put the 'new' coil above on today and it started straight away. So, I have another of these coils from Thailand already, and will do the same with the one I took off, ready for the other bike. We have hit upon a good thing here. I am no doubt far from the first person to do this mod, but I haven't read about it anywhere so I thought we should share the idea.

There is a way of modifying the ignition to improve it with a transistor based set up. There are details of it available HERE.