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<p>That is a late internal inductive pickup so probably negative
earth. It has male and female bullets for two white wires, the
wrong way round the tach won't work and the right way it should
but original the gender of the wires was correct for the
internals. The spade is for 12v. They were used on the MGB until
the 1973 model year so could be either positive or negative earth,
usually printed on the dial, but positive could have been
converted to negative by a PO.</p>
<p>From 73 voltage triggered tachs were used with a single
white/black wire from the coil -ve to a single bullet on the back
of the case with the spade for the 12v supply, earth again either
a spade on the case or a black wire under one of the fixings. All
negative earth of course.</p>
<p>The tach 12v feed comes from the voltage stabiliser as that is
just a convenient point for picking up the 12v supply rather than
going all the way back to the fusebox. It is a green wire i.e.
fused ignition that feeds the stabiliser as well as the tach,
power is not passing through the stabiliser to the tach.</p>
<p>PaulH.<br>
</p>
<p></p>
<div class="moz-cite-prefix">On 23/10/2024 20:25, dave northrup
wrote:<br>
</div>
<blockquote type="cite"
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<p class="MsoNormal"><span style="color:black">Working on an MGA
with a swapped in early 5 main MGB engine.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">Trying to figure
out how to set up an electric tach. With the car came an
MGA tach with the internals swapped for an MGB tach but it
doesn’t work. I purchased an MGB tach, and am trying to
test it before I attempt to swap the internals for the non
working one.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">Here is a picture
of the tach; there are 2 white leads, which according to the
wiring diagram, one goes to the coil and one to the
ignition. Which is which? Or should I just try them? I
know that it goes power to tach to coil. We had the car
running with the old tach but no movement of the needle
before we found out that the gage was bad.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">Also, I am
assuming the extra spade in the tach goes to power? At
least the ground spade is obvious as its part of the case.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">And, while I’m at
it, the MGB wiring diagram shows one lead to the gage
voltage stabilizer. I’m thinking that can go directly to
the fuse box to power?<o:p></o:p></span></p>
</div>
<br>
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