Doug,
You are correct that there is twelve volts there,
but the points closing the resistor/coil circuit to
ground causing the primary to charge, then discharge
when the points open, causes the magnetic field in
the coil primary to collapse. This magnetic field
change is multiplied many times by the secondary
windings, producing the spark at a very much higher
voltage.
As this occurs, the current in the line goes from
zero to max. and back to zero. This current pulse
is fed through the current sensing tach (with it's
on little coil) and that makes the tach work.
It doesn't take a rocket scientist.....
{9->
Steve
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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