Subject: Re: [Mgs] MGA with 5 main MGB engine

From: Paul Hunt <[email-masked]>
Date: Sun, 30 Jul 2023 10:07:52 +0100

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Which tach?  Where did it come from?

For an MGB tach 'yes' if it has RVI on the dial.  No if it has RVC, for 
that you need a wire back from the points side of the coil to the tach 
bullet connection.

Plus 12v and earth connections to the tach to power the electronics, and 
that raises further questions. Have you converted the car to positive 
earth? If not unless the tach is already negative earth (the _original_ 
polarity is also on the face of MGB tachs for example) you will need to 
reverse the power wires inside the tach case and also the signal wires, 
which can be inside the tach or outside depending on which tach you have.

PaulH.

On 30/07/2023 01:50, dave northrup wrote:
>
> I am trying to figure out how to connect the tach on this car.  it 
> came to me in kit form
>
> This diagram seems to show that in essence the connection from power 
> to the ignition coil goes through the tach.  That green wire goes off 
> to the gage voltage stabilizer – is that even needed?
>
> So it seems to me that on my car, which has an original early  MGA 
> wiring harness, all I really need to do is run the white wire through 
> the tach then to the ignition coil, instead of going straight to the 
> ignition coil.  Am I on the right tach here (haha)?
>
>
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>
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    <p>Which tach?  Where did it come from?<br>
    </p>
    <p>For an MGB tach 'yes' if it has RVI on the dial.  No if it has
      RVC, for that you need a wire back from the points side of the
      coil to the tach bullet connection.</p>
    <p>Plus 12v and earth connections to the tach to power the
      electronics, and that raises further questions. Have you converted
      the car to positive earth? If not unless the tach is already
      negative earth (the _original_ polarity is also on the face of MGB
      tachs for example) you will need to reverse the power wires inside
      the tach case and also the signal wires, which can be inside the
      tach or outside depending on which tach you have.</p>
    <p>PaulH.<br>
    </p>
    <p><br>
    </p>
    <div class="moz-cite-prefix">On 30/07/2023 01:50, dave northrup
      wrote:<br>
    </div>
    <blockquote type="cite"
      cite="mid:[email-masked]">
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        <p class="MsoNormal">I am trying to figure out how to connect
          the tach on this car.  it came to me in kit form<o:p></o:p></p>
        <p class="MsoNormal"><o:p> </o:p></p>
        <p class="MsoNormal"><img style="width:5.9916in;height:2.5583in"
            id="Picture_x0020_1"
            src="cid:[email-masked]" class=""
            width="575" height="246"><o:p></o:p></p>
        <p class="MsoNormal"><o:p> </o:p></p>
        <p class="MsoNormal">This diagram seems to show that in essence
          the connection from power to the ignition coil goes through
          the tach.  That green wire goes off to the gage voltage
          stabilizer – is that even needed?<o:p></o:p></p>
        <p class="MsoNormal"><o:p> </o:p></p>
        <p class="MsoNormal">So it seems to me that on my car, which has
          an original early  MGA wiring harness, all I really need to do
          is run the white wire through the tach then to the ignition
          coil, instead of going straight to the ignition coil.  Am I on
          the right tach here (haha)?<o:p></o:p></p>
      </div>
      <br>
      <fieldset class="moz-mime-attachment-header"></fieldset>
      <pre class="moz-quote-pre" wrap="">_______________________________________________

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From: PaulHunt73 <[email-masked]>
Date: Sun, 30 Jul 2023 10:19:58 +0100

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Obvious correction - I assume the MGA would be positive earth originally 
like early MGBs, so it should read "Have you converted the car the 
negative earth" if the tach you have is a negative earth.

On 30/07/2023 10:07, Paul Hunt wrote:
> For an MGB tach 'yes' if it has RVI on the dial.  No if it has RVC, 
> for that you need a wire back from the points side of the coil to the 
> tach bullet connection.
>
> Plus 12v and earth connections to the tach to power the electronics, 
> and that raises further questions. Have you converted the car to 
> positive earth? If not unless the tach is already negative earth (the 
> _original_ polarity is also on the face of MGB tachs for example) you 
> will need to reverse the power wires inside the tach case and also the 
> signal wires, which can be inside the tach or outside depending on 
> which tach you have.
>
> PaulH.
>
>
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    <p>Obvious correction - I assume the MGA would be positive earth
      originally like early MGBs, so it should read "Have you converted
      the car the negative earth" if the tach you have is a negative
      earth.<br>
    </p>
    <div class="moz-cite-prefix">On 30/07/2023 10:07, Paul Hunt wrote:<br>
    </div>
    <blockquote type="cite"
      cite="mid:[email-masked]">
      <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
      <p>Which tach?  Where did it come from?<br>
      </p>
      <p>For an MGB tach 'yes' if it has RVI on the dial.  No if it has
        RVC, for that you need a wire back from the points side of the
        coil to the tach bullet connection.</p>
      <p>Plus 12v and earth connections to the tach to power the
        electronics, and that raises further questions. Have you
        converted the car to positive earth? If not unless the tach is
        already negative earth (the _original_ polarity is also on the
        face of MGB tachs for example) you will need to reverse the
        power wires inside the tach case and also the signal wires,
        which can be inside the tach or outside depending on which tach
        you have.</p>
      <p>PaulH.<br>
      </p>
      <p><br>
      </p>
      <div class="moz-cite-prefix">On 30/07/2023 01:50, dave northrup
        wrote:<br>
      </div>
      <blockquote type="cite"
        cite="mid:[email-masked]">
        <meta http-equiv="Content-Type" content="text/html;
          charset=UTF-8">
        <meta name="Generator" content="Microsoft Word 15 (filtered
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          <p class="MsoNormal">I am trying to figure out how to connect
            the tach on this car.  it came to me in kit form<o:p></o:p></p>
          <p class="MsoNormal"><o:p> </o:p></p>
          <p class="MsoNormal"><img
              style="width:5.9916in;height:2.5583in"
              id="Picture_x0020_1"
              src="cid:[email-masked]" class=""
              width="575" height="246"><o:p></o:p></p>
          <p class="MsoNormal"><o:p> </o:p></p>
          <p class="MsoNormal">This diagram seems to show that in
            essence the connection from power to the ignition coil goes
            through the tach.  That green wire goes off to the gage
            voltage stabilizer – is that even needed?<o:p></o:p></p>
          <p class="MsoNormal"><o:p> </o:p></p>
          <p class="MsoNormal">So it seems to me that on my car, which
            has an original early  MGA wiring harness, all I really need
            to do is run the white wire through the tach then to the
            ignition coil, instead of going straight to the ignition
            coil.  Am I on the right tach here (haha)?<o:p></o:p></p>
        </div>
        <br>
        <fieldset class="moz-mime-attachment-header"></fieldset>
        <pre class="moz-quote-pre" wrap="">_______________________________________________

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