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Hi everyone! I'm brand new to this forum and only a month into owning a 1975 Honda xl250, but I'm no newbie to wrenching or to the bike model. I grew up learning to ride on a 74 xl250 and have become a motorcycle and jeep gearhead.

I look forward to spending some time getting to know you guys and learn about this bike. My question is this: I've been making repairs and base-lining this old bike but have never worked with 6v electrical systems. This bike seems to run both on AC and DC, depending on the circuit.

So....I found a tail light assembly on ebay (mine was from some early 80's sport bike) and wired it in last night. The taillight functions but when I apply the brake the light dims and nearly goes out. I tested for DC voltage and got wierd readings. I tested for AC and found 2 volts. I tested at the battery and found at idle there were 2V. If I revved it to 4kRPM, the charge to the positive side of the battery climbed to 5.5V, and the brake light brightened greatly.

The battery is shot and I tested the rectifier per my Clymer manual with ambiguous results. Two questions: is there a seperate voltage regulator on this model (conflicting info on this), and shouldn't the battery be charging at more like 7-8V at high RPM? How's a 6V battery ever going to reach full charge when it's only receiving a max of 5.5v??

Thanks for reading and I'm looking forward to getting to know you all!

Jeremy

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Jeremy:

 

Your gonna need a wiring diagram and some careful study.  Look at your wiring diagram.

 

You will see there is 3 separate circuits on this bike, coming from 3 separate generating coils.   One coil runs the headlight with raw AC.  Also hooked to the headlight wire is an AC regulator that clips the raw AC so the headlight doesn't get burned out.  

 

A second coil that isn't grounded to the case (floating) has two wires (lavender and yellow) to a full-wave rectifier and DC regulator that charges the battery.  The battery powers the other lights and flashers, and the horn.  If the battery is shot it will drag down the voltage from the rectifier and the voltage will be low. Also, remember the voltage is AC on the two charging lines to the regulator, and then is pulsing DC.

 

A 3rd coil is grounded to the generator case and the single live wire (Brown) runs the CDI.  This would also be an AC voltage that is rectified and processed by the CDI to run the ignition.

 

Measuring raw AC voltage on a bike is a crapshoot because the waveform is not a smooth sine-wave at 120 hz, and most meters have a problem.  If you need a new battery, install one, the charging system can't work without it.

 

 

Just some shots in the dark....

 

patuca

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Another point, you cannot accurately test the charging system if the battery is bad. You must use a good, fully charged battery to get an accurate charging voltage. Typical values for a 6V battery at rest (key off) is 6.4 volts. Key on, it will drop to about 6.2 (tail light on only). Engine running, it should rise over 6.4 volts. At 4,000 RPM, you should get as much as 7.4 volts. It should not rise much above (if at all) if the revs climb further.

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Thanks for the warm welcome and helpful advice. I'm working though Patuka's info currently, and replying from my phone is a pain.

When I get home tomorrow, I'll buy a battery and go from there. As far as identifying the three described charging circuits, it'll take some work to figure that out.

So if I understand correctly, I can check for the DC current just as I would a 12V system. How do I check AC? Test light only? It doesn't sound as straightforward as testing for household 110V with a multi-meter...

I'll check back in with an update soon.

Edited by 1978jeep258
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So, an update. I've studied the wiring diagram and worked through many of the concepts. A few questions remain: I still don't know for certain if there's a regulator seperate from the rectifier, but I'm starting to become convinced one exists per the wiring diagram. Second, I don't see the seperate regulator on the diagram for the headlight that you mention, Patuka.

I'll know more in coming days as I purchase a new battery and continue diagnosis. Thanks again, all of you, for the help. Jeremy

PS, there's no CDI, just points. But I'd like to know if there's a way to convert to electronic ignition!

Edited by 1978jeep258
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Hi Jeremy:

 

The diagram I thought was right is this one...

 

http://carwiringdiagram.net/diagrams/16/2008/07/Honda-XL250-Wiring-Diagram.jpg 

 

If your bike has points then this infomation is wrong and  I can only advise you to 

try the new battery and go from there.....I searched and found another diagram here....

 

http://www.cmsnl.com/classic-honda-fansite/honda_wiring_diagrams/XL350.jpg

 

If that's the case I can't help much because I'm not familiar with that system although it appears the headlight

does work off the battery on that system.   Good luck.

 

 

 

good luck.

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Patuka,

 

I installed a new battery, which solved some of my initial problems:  The brake light works now and is bright.  The neutral light activates now too.  I am still tracking down the turn signals and it appears the low beam is burned out.  I'm pretty confident from everything I've read that the headlight has nothing to do with the battery, but your second diagram does show a regulator, which I have not yet located.  I've also not located any photos of a regulator for this model.

 

Interestingly, my manual wiring diagram indicates the AC to the headlight has the voltage run through a resistor to accomplish a low beam.  As if that would be necessary!  Mine is missing, which may have been the cause of the low-beam burning out.  I've not located any more info on the headlight resistor and don't know what it looks like.  The only thing I've learned is that it's supposedly a 3.61OHM resistor.  No wattage listed and no part number.  

Sorry for the thread creep, but this electrical system seems crazy to me!  Working through its issues though and thanks for the help.

 

Jeremy

Edited by 1978jeep258
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To summarize...

 

1)  Does a 73-75 XL250 have a voltage regulator (the device that restricts voltage to approximately 6 volts, not to be confused with the rectifier, which converts AC to DC)

2)  If so, can someone post a photo or diagram showing its location?  

3)  Can someone take out their headlight and show me what the white wires are connected to?  One comes into the bucket and splits at a connector to a) the headlight and B) a resistor of some sort.  I need more info on the resistor please.

 

Thanks in advance and you've got a great forum here!

Jeremy

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