BDurgin1@aol.com wrote:
> Can someone explain to me why this unit will only work
> with a negative ground?
Not for any real electrical engineering reason,
just for a physical one.
The unit is basically a metal disc with a black epoxy
cube on it. The cube contains both the sensor and
the electronics, all in one.
Only two wires come out of the epoxy cube, essentially
power and the switched signal. The unit relies on the metal disc
being in contact with the distributor, to the engine,
to the ground strap, and to the chassis ground.
So there is no reason why the pertronix couldn't have
been built to work negative ground, it's just that
it was designed to have only two wires, and ground
physically, and the electronics inside rely on
the physical ground being negative with respect to
the power wire.
The same pertronix "cube" is put on hundreds of
different mounting disks to work in distributors for
a really large number of cars. I guess the total
percentage of cars out there that need a negative
ground model hasn't been large enough to convince
the company to re-engineer a new version of the cube.
Contrast this with other systems like the crane/allison
unit. Only the sensor goes into the dizzy, the
rest of the electronics live outside the unit
in a generic-style finned case. The finned case
is different for positive ground, but the sensor
is always the same.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
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