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  1. #1
    CB750 Member diggidan's Avatar
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    Honda cb750 -71 electrical question

    Hi guys!
    I have a cb750 from 1971 and I'm going to change out the rectifier and regulator to one combined thingamagig. I don't have any electrical scheme of the new box.

    Now the problem is that the colors of the new box dont correspond to the colors coming out of the engine.

    From the engine I have the colors:
    3 Yellow
    White
    Green
    Light green / red
    Blue / red

    And in the box has:
    3 Yellow
    Red
    Green
    And out from the box comes:
    Black
    White

    I know that the LG/R and B/R is neutral and oil from the engine.
    And the yellow ones are quite self explanatory but the question is:

    Do I connect the green from the engine with the green on the box? As far as I can understand the green is earth from the alternator?
    And do I connect the white from the engine to the red on the box?

    I have gone through the electrical scheme but I can't figure out what the white from the engine is...

    Very thankful for any insights!

  2. #2
    Moderator dirtdigger's Avatar
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    I would contact the company that you bought it from, they should have a diagram and be able to tell you what the wires from the box go too. You never know how they wired the box and what wires go to what.

  3. #3
    CB750 Guru amc49's Avatar
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    X2, you must know what every single one of those wires does or a very good chance you may even burn bike to the ground.

    White coming from the engine is the field coil supply to the alternator coil for magnetism. It is bolted to the inside of the case cover.

  4. #4
    CB750 Member diggidan's Avatar
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    Quote Originally Posted by dirtdigger View Post
    I would contact the company that you bought it from, they should have a diagram and be able to tell you what the wires from the box go too. You never know how they wired the box and what wires go to what.
    I have contacted them but they can't get a schematic they say... I probably should have checked that before I bought it... So now I'm back to square one I'm afraid.

  5. #5
    Moderator dirtdigger's Avatar
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    How do they expect you to hook it up if they dont give instructions or help with wiring? Can you return the item? If they are unwilling to help then get you money back and go back to the stock stuff or get one from a reputable company...or at least one that will help with wiring.

  6. #6
    CB750 Member diggidan's Avatar
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    Quote Originally Posted by dirtdigger View Post
    How do they expect you to hook it up if they dont give instructions or help with wiring? Can you return the item? If they are unwilling to help then get you money back and go back to the stock stuff or get one from a reputable company...or at least one that will help with wiring.
    Unfortunately I can't return it but they sent me a really good reply: "If necessary, please have it installed professionally in a workshop.
    Otherwise you can also google."
    Hahaha, real professionals.
    I guess I must be able to measure the voltage and stuff somehow if I just connect the three yellow wires.
    They are the only ones that is self-explanatory.

  7. #7
    Moderator dirtdigger's Avatar
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    post a picture of your regulator and of the connector and wire colors

  8. #8
    CB750 Member diggidan's Avatar
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    Quote Originally Posted by dirtdigger View Post
    post a picture of your regulator and of the connector and wire colors
    So the wire colors in the connector is:
    Yellow
    Yellow
    Yellow
    Green
    Red

    And then:
    Black
    White
    By themselves

  9. #9
    Moderator dirtdigger's Avatar
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    Is this picture exactly how yours is?

  10. #10
    CB750 Member diggidan's Avatar
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    Quote Originally Posted by dirtdigger View Post
    Is this picture exactly how yours is?
    Yes indeed! But I've cut the connector of because it of course didn't fit the two connectors from the engine.

  11. #11
    Moderator dirtdigger's Avatar
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    All I can do is guess, most of the stock ones I use have another black wire that yours doesnt. Even the aftermarket ones I have looked at have another wire yours doesnt. Yellows are self explanatory. Black goes to white on bike, white goes to green on bike. Green is battery negative, red is battery positive. Normally on the others I have seen the extra black goes to ignition switch. Again this is what I can guess based on my experience but then again yours is not the same as what I use or have seen. I would say you should maybe take the red to a switched power and not directly to the battery.

  12. #12
    CB750 Member diggidan's Avatar
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    Quote Originally Posted by dirtdigger View Post
    All I can do is guess, most of the stock ones I use have another black wire that yours doesnt. Even the aftermarket ones I have looked at have another wire yours doesnt. Yellows are self explanatory. Black goes to white on bike, white goes to green on bike. Green is battery negative, red is battery positive. Normally on the others I have seen the extra black goes to ignition switch. Again this is what I can guess based on my experience but then again yours is not the same as what I use or have seen. I would say you should maybe take the red to a switched power and not directly to the battery.
    Thank you so much for the guess!
    The wierd thing I think is that the black and white is a smaller gauge wire than the other's.
    But I'll try it your way and will hook it up in stages to be able to measure the voltage and such.
    Thanks again man! Much much appriciated!

  13. #13
    Moderator dirtdigger's Avatar
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    Black and white only serve to activate the field coil, very little electric load

  14. #14
    CB750 Member diggidan's Avatar
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    Quote Originally Posted by dirtdigger View Post
    Black and white only serve to activate the field coil, very little electric load
    Ahaaa!
    Well, thanks again man! Will come back to inform if it has been a success or not, hehe.

  15. #15
    Moderator dirtdigger's Avatar
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    If you are really concerned you could protect the wires with inline fuses temporarily till you know it is wired correct.

  16. #16
    CB750 Member diggidan's Avatar
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    Quote Originally Posted by dirtdigger View Post
    If you are really concerned you could protect the wires with inline fuses temporarily till you know it is wired correct.
    Good idea!

  17. #17
    CB750 Guru amc49's Avatar
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    The YHC-104 on the side identifies it as a Yamaha XV750 or XV920 regulator, dig up Yamaha wiring diagram and then apply the colors to the Honda as interpretation.

    Personally, I would not buy anything from somebody stupid enough to not be able to tell you what it is.

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