Vintage Dirt Bike Q & A

Hey there can someone tell me if their is a link to a basic wiring dig. for a 77 mr175.
Thanks

This is from the '77 MR175 owner's manual:

Just FYI - the bike runs just fine with the rectifier removed. Just connect the Black/Yellow and Black/White wires together, and leave the Green ground wire disconnected.

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

What about a '74 MT250? Anyone have any diagrams?

I think this is for all years of MT250:



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

Thanks a million! I may be able to begin troubleshooting...

Wow the MT is a bit more complicated huh?

Yes, it really is. ;>)

Are you looking to get your lights etc. working again, or are you just curious why they don't work? I ask because it can be a fair amount of work to troubleshoot an electrical system that was working normally yesterday; one that's been intentionally disabled - as apparently yours has - can be a real nightmare. You really have to assume from the start that every bulb is bad, every switch doesn't work, every wire has been cut, etc. - otherwise you'll probably just end up chasing your tail.

Do you have a meter?

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

Ray,
Thanks for the time in responding to my posts. I bought the bike to use as a hunting/scouting vehicle....here in Arizona we have lots of backroads trails. I could care less about the instrumentation, horn, etc. I do care about the headlight though. I will need it while riding in the early mornings and near evenings. So, the bottom line, I just want my headlight to function. But it is wierd, nothing works properly on the gauge cluster. No lights at all....any ideas or tricks to get just the headlight working? Why would have all the bulbs blown out?

Forgot to add I do not have a multimeter...but can get one from my father in law....

Well, it could be so many things. On the diagram, try chasing the wire coming out of the main lighting coil (it's between the YELlow and PINK wires, and is unmarked at that location but may be white with a yellow tracer) all the way to the headlight bulb - anything you encounter along the way could be bad, including the lighting coil itself. Bear in mind that both light switches have to be good for the headlight to work.

This is why I asked about the meter - when a system is in this state of disrepair, it's really easiest to assume the worst and start from scratch. With a meter set to ohms, you could connect one lead to the headlight 'hot' wire and one to ground, and check everything including the lighting coil in about one second, with the motor off. If the lighting coil isn't working, nothing else matters 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

Ray, problem solved. See my post under 74 MT250 Electrical. It was just the HI/LO beam switch.......haha...LET THERE BE LIGHT!!!

Good stuff.

Just one pointer. These bikes do NOT have any voltage regulator. The MR runs all lights non-rectified, meaning they are AC voltage and go brighter with RPM, and all bulbs must be connected and working, otherwise the remainder will pop at high RPM when turned on. As one bulb burns out, all the other bulbs pop fast in succesion.

The MT bikes run the headlight and the instrumentation lights off the generator and are, just like the MR, not regulated, nor rectified.
The tail, brake and signals are rectified, but only regulated by the current they require, meaning the arnature/generator can only create so much current. The battery becomes the limiter so to speak.