On Sun, 17 Feb 2019 16:20:16 -0600, Fox's Mercantile
wrote:

On 2/17/19 2:11 AM, wrote:
It does seem kind of bizarre that the (+) terminal is used for the high
voltage return, (knowing that spark plugs complete the circuit by being
connected to the engine block, which is connected to the battery
GROUND).

The internal resistance of a car battery is close to zero ohms.
When the points open, the magnetic field from the primary collapses.
This causes a huge inductive kick voltage spike. The condenser across
the points acts like a tuned circuit to sustain the high voltage by
acting like a tuned circuit. The secondary being in series with the
primary acts like a auto-transformer and increases the high voltage
oscillations to a value high enough to create a solid, hot, spark
across the electrode of the spark plug.

The fact that the return is via the positive terminal of the battery
doesn't mean ****.
I was taught years ago that the condenser was to prevent arcing at the
points. It was not until recently I learned that its more important
function is to be part of a tuned resonant circuit. This makes so much
sense. About 40 years ago I had a motorcycle ignition problem that was
fixed by replacing the condenser and I never knew why. I still don't
know why Lucas ignitions used a rising field ignition instead of the
usual collapsing field. And I knew lots of guys who converted their
British bikes to rising field ignitions for the better spark. Me
included.
Eric