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Thread: wiring help, SWB early 1971 R75/5 (engine harness wiring with alternator)

  1. #1

    wiring help, SWB early 1971 R75/5 (engine harness wiring with alternator)

    Hi everyone.

    I think I need some visual help
    Here is a picture of my 1971 R75/5, front motor wiring with the alternator harness

    As I look for images on the internet
    I find many pictures on newer bikes
    they have a Y harness that connects to the alternator body, and then the diode board

    I went through all of my boxes from disassembly 3 years ago
    I do not have that harness (used) from disassembly

    also... this early stock alternator does not have the electrical connection to mount the Y harness

    it has occurred to me that possibly a previous owner removed the bolt on connector and removed the old harness prior to my ownership
    but what seems more likely is that this early (non fused) bike may have had different wiring for the Diode board


    additionally....
    I now feel like I need to confirm the wiring on my diode board now.
    I have the large (Left side when facing forward with the bike) connector on the left of the diode board (large spade)
    Next to the large spade I had an open terminal

    but on the opposite side... (Right when facing with the bike) the spade is open on my diode board
    it looks like something needs to go there... but I don't have a harness and can't figure out what


    can anyone post a picture or two of their early non fused wiring in the front chest (points/alternator area)

    thank you in advance
    brant
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  2. #2
    Liaison 20774's Avatar
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    Anton has a picture of several versions of the OEM board:

    http://largiader.com/articles/charging/

    It does appear per his pictures that you have the /6 style board with an open "Y" or center tap. He indicates that in this configuration, without using the center tap being utilized in your case, it's the same output as the earlier /5 board. This additional tap was for higher output...I'm not sure if having the tap means there's more power there to be had or it "might" be there if you were to upgrade the alternator.

    Snowbum also mentions it on this page:

    https://bmwmotorcycletech.info/trbleshootALT.htm

    Search the page for "wye" which is the Y connector. He does mention that in order to get the additional alternator output, you would /6 type equipment (stator, rotor, etc.).
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Quote Originally Posted by 20774 View Post
    Anton has a picture of several versions of the OEM board:

    http://largiader.com/articles/charging/

    It does appear per his pictures that you have the /6 style board with an open "Y" or center tap. He indicates that in this configuration, without using the center tap being utilized in your case, it's the same output as the earlier /5 board. This additional tap was for higher output...I'm not sure if having the tap means there's more power there to be had or it "might" be there if you were to upgrade the alternator.

    Snowbum also mentions it on this page:

    https://bmwmotorcycletech.info/trbleshootALT.htm

    Search the page for "wye" which is the Y connector. He does mention that in order to get the additional alternator output, you would /6 type equipment (stator, rotor, etc.).


    thank you again Kurt
    I'll read both of the links...

    "Wye" connector... learned something new today


    so possibly a previous owner replaced the dio board with a newer 74 style board
    but sounds like the early alternator without the additional connection... is going to be low output unless changed... no matter which board
    thats fine... Its stock wiring anyways...
    I'll run with low output

    now, I just need to do more research about the wiring routing.. or find a picture
    but thank you for helping me learn... and I will leave that post empty on the dio-board since I have the early alternator

    brant

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