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  1. #1
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    Default Alternator connection for tach

    My engine has had a replacement alternator installed by the previous owner and the tachometer doesn't work at present. This alternator has only three connections - B, L (light, I think), and R (field, I think). My understanding is that to connect up the tachometer from the switch panel it needs a fourth connection (usually w) and this is shown in the engine wiring diagram (below).

    Is this true? Or do I just use one connection - R?

    I am a bit confused because the diagram seems to show the tach connected to both R and W:

    http:www.pinksgreen.com/wiring.pdf

    Any advice welcome.

    Philip

  2. #2
    earlybird is offline Registered User
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    Your link doesn't appear to work. I would think that the "R" terminal is connected to the internal regulator, and extenally to the "ignition switch. (It is for Hitachi alternators anyway).
    IMHO, you need a dedicated tacho "W" terminal to give the necessary AC output. The other terminals connect to the battery one way or another and will not give the frequency signal.

  3. #3
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    Link seems to be working for me - it is: http://www.pinksgreen.com/wiring.pdf

    Alternator is a Mitsibushi 50A 3 wire alternator. Should have said that.

    Philip

  4. #4
    VicS is offline Registered User
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    Quote Originally Posted by dgadee View Post
    Link seems to be working for me - it is: http://www.pinksgreen.com/wiring.pdf

    Alternator is a Mitsibushi 50A 3 wire alternator. Should have said that.

    Philip
    Thats better, dunno why the first link does not work.

    The signal to the tacho comes from the W terminal via wire 10 in the diagram

    It is a direct connection to one of the stator coils. Ie it is unrectified AC.

    Sometimes it is a tapping off the coil to deliver only 8 volts I beleive.

    Other connections to the tacho are the positive and negative power supply and to the illumination bulb.

  5. #5
    earlybird is offline Registered User
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    For some reason, the 2nd link works for me. Don't understand why wires 10,11 and 12 all seem to be joined at the connector, perhaps I'm misinterpreting.
    I would expect the tach to have a 12v power connection, + & -, and a separate signal, (W) connection.
    Perhaps someone else can expain.

  6. #6
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    I think I get it now. Will take it over to my car electrics man and see whether he will add a w connection to it for me.

    Thanks,

    Philip

  7. #7
    VicS is offline Registered User
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    Quote Originally Posted by earlybird View Post
    For some reason, the 2nd link works for me. Don't understand why wires 10,11 and 12 all seem to be joined at the connector, perhaps I'm misinterpreting.
    I would expect the tach to have a 12v power connection, + & -, and a separate signal, (W) connection.
    Perhaps someone else can expain.
    Yes you are misinterpreting the representation of the 12 way connector

    Tach connections explained while you were posting

    The one bottom right goes via wire 5 to earth . the one bottom left is the positive ...
    Last edited by VicS; 05-04-11 at 21:31.

  8. #8
    earlybird is offline Registered User
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    Quote Originally Posted by VicS View Post
    Yes you are misinterpreting the representation of the 12 way connector

    Tach connections explained while you were posting

    The one bottom right goes via wire 5 to earth . the one bottom left is the positive ...
    I'll defend myself; that's what it should be in reality, and that's what I said I'd expect, but it's not what the diagram shows. eg; upper right teminal on "B" appears to indicate wires 10, 11 &12 all connected to the same terminal. Lower left on "A" shows 10 & 12 apparently connected. That was part of the OP's problem I think.
    Must have been drawn by the apprentice draughtsman.
    Last edited by earlybird; 05-04-11 at 21:46.

  9. #9
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    It is for a vetus m3.10, so presumably a Dutch apprentice.

  10. #10
    earlybird is offline Registered User
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    Quote Originally Posted by dgadee View Post
    It is for a vetus m3.10, so presumably a Dutch apprentice.
    Or maybe double dutch.

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