All this is dealing with my Sportster:

Had a bit of fun earlier. Ran out of gas coming home from work. Long push down the highway to the gas station. I'm glad that bike is so light.

Gassed up and on my way, look down, and my (electronic) speedometer is cutting in and out. Thanks to the magneto, the motor was still running fine, but my other electrical power is glitched. Got home, and observed that odometer registered about five miles where it normally would have been about 12.

I can't imagine how the whole running out of gas thing isn't anything other than a pure coincidence, but thought I'd mention it.

Recall that I am running the stock rotor/stator into the stock VR. From there, it's all custom wiring going to the tail light, the brake light, the head light and the speedometer.

Back home. Ate dinner. Gave it a think. Went out to the garage and started the bike. Lights and speedometer worked fine.

Pulled the connector between the stator and the VR. Measured 20 VAC (more or less) at idle. Measured 75 VAC (more or less) when I spun up the motor.

Plugged the stator back into the VR. Measured something like 12 VDC at idle (it's a pretty low idle, but don't have a tach, so I can't say exactly what it is) between the VR output and the frame. Spun up the motor and the VDC dropped. That is such a weird result that I question if I was doing something wrong on the test.

Measured something like 5 VAC between the VR output and the frame.

Checked to see if the stator was shorted: Passed on both leads.

Something else to note: Over the last however many hundreds of miles, I've noticed that the headlight will dim when I'm at speed (going 50 MPH down the road, for example), but then brighten up when I hit the brake (and therefore activate the brake light). I really don't know when that started. I don't ride at night that much and it very well may have done that from the start.

Anyway, after running the tests, and with the electrical seeming to be working fine in the garage, took her around the neighborhood a bit for a road test. After a few minutes (lets say a mile down the road), the same symptoms I experienced earlier on my ride home returned.

Another thing to note: When I was putting this together a few months ago, I couldn't get any of this to work until I hooked up the headlight. It was as if the VR needed a certain resistance load on it before it would "wake up".

Anyway, based on all of the above, I'm leaning toward the opinion that the VR is shot.

But I'm also wondering if I killed it because of the way I've got this thing set up. The way the lights dim, then brighten when the brake light comes on, makes me wonder if I should install a resistor somewhere in the system just to increase the load.

Any thoughts, advice or ideas?

 

Just because a part burns out don't think it is reoccurring problem until it starts reoccurring.

 

You've probably already checked and doublechecked this, but every time I've had weird electrical things happening on a car or truck or boat trailer or whatever, it's usually caused by a bad ground somewhere. Something isn't grounded that should be, or it isn't grounded well enough to work properly. (i.e. ground wire is too small, or there's paint/rust/powdercoat, corrosion, etc. causing poor current flow.)

I'd be curious to know if when you step on the brake and the headlight brightens up, is the voltage to the headlight increasing to make it brighter? Or is the brake circuit somehow improving the grounding of the headlight circuit so more current can flow through the headlight?

I don't know what to make of the 5v AC between VR output and frame, or the voltage dropping when you rev up the bike. That may be a bad VR, dunno.

 

I'm inclined to agree that there is an electrical gremlin at work. Further to YK's suggestions, it only needs a little overnight condensation for an iffy connection to get some corrosion and hence increase resistance. It's long enough since your build for something like that to show it's head. In wiring your bike did you consider using one of the modern modular systems, like Motogadget? A pal has used on on his Glide and it certainly simplified the wiring a great deal. I realise your wiring is also probably very simple!

 

Correct me if I'm wrong, but isn't 75 vac @2000 rpm way too much? shouldn't there be like 30 -33 vac? I'm inclined to think that the VR is doing what it should be shunting off the excess or over volting Alternator. That's why at Idle or 5 vac the lights seem to operate at full lumens and at Higher rpm or higher vac (75) the regulator is protecting the battery... I think there is something funky going on with the rotor or stator. Maybe the magnets shifted in the rotor...

 

I think the regulator is shot.

 

Connections. When you put the break light load on and the headlights get brighter, that is from the load heating up the bad connection and making it better

 

I don't get the magneto part of the description... as that would be an old Ironhead... But..
If you have a Spare or just another battery try that First.., then the Regulator..
Batteries can go bad in Many Ways...
Voltage regulator may then, and only then, be suspect..
75VAC is Too Much, but the 24+ is good at idle..for the Stator output..
I would run the thing for a test ride without the Stator plugged into the VR... Total loss.. split the system so to speak..
You'll be surprised how far you can get without a Charging system... if ya have a reasonable battery..

 

I'm pretty sure it is because you are not running a battery...did you try a battery eliminator?

https://www.jpcycles.com/product/381...AaArVcEALw_wcB

 

That item of info seems to be missing! Or simply add a small battery, like one off a small scooter. I did that on my Greeves Enduro many years ago, to keep the lights alight. 0maha could put it in his pocket if he wants to keep weight off the bike.....