Vintage Dirt Bike Q & A

1974 Honda MT250.

Ok I'm looking for the resident electrical system genius. My headlight was not working but the bike ran fine. After a bunch of troubleshooting I determined there was no juice coming to the light from the generator as the bulb and switch were good. I then tested the stator coils and indeed one was bad (the one that charges the battery that connects to the pink and yellow wires going to the rectifier). So I disassembled the bike and began a fruitless search for a replacement stator assembly. One company I contacted wanted $150 to rewire just the bad coil. I'm very handy so I decided to take up the challenge myself. A used stator if you can find one on ebay goes for $100 - $150. I want to re-build the whole thing and fix it once and for all so I don't have to mess with it anymore.

Ok so here's the problem. In the process of disassembling the stator assembly to determine what parts I would need I unwrapped the coil completely but failed to take note if it was wound clockwise or counter clockwise. The other 2 coils are intact so I can still copy them. The other 2 coils are wired together to run the ignition and one is wound with 16 AWG wire clockwise while it connects to a coil wound counter clockwise with 20AWG wire.

I'm thinking for the coil in question it will not matter as the rectifier is converting the AC to DC anyway but I am not sure. I'm also thinking if I wind it the wrong way and there is a problem making "negative" voltage then I can simply switch the leads to the rectifier after the fact.

I don't want to spend too much time on this project only to find I wasted my time and money.

I hate electrical shit. Give me the mechanical problems!

Any suggestions on my project are appreciated.

Thanks Rob

Rob,

Maybe this will help a bit until the resident genius weighs in... It's been a while since I've seen an MT250 stator, but according to the wiring diagram there should be a coil with a white/yellow wire and the other coil end grounded (headlight coil, straight AC to the bulb through two separate switch setups) wound with fairly heavy-gauge wire, another coil with yellow and pink wires (AC to the rectifier for battery charging and all bulbs other than the headlight) wound with similar wire, and the ignition source coil (black/white wire, one end grounded) wound with more turns of finer-gauge wire.

In this circuit, it shouldn't matter which direction the coils are wound. I don't know if you use the headlight much, but if so this might be an opportunity to rewind the lighting coil for an alternative headlight (LED, 12V, etc.) if desired.

Perhaps you've already done so, but I would take a resistance reading from the lighting coil ground to the headlight bulb socket. There's a lot going on between these two points, and if you see an open circuit the coil won't matter much.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric