In spring 2001 my 1967 Simplicity 2012 tractor wouldn't start. It had
no spark, After replacing points, condenser and spark plug, and
checking the wiring and connections, still no spark, so the failed
component had to be the magneto.

Replacing the magneto would require removing the 12 horsepower engine
from the tractor, a daunting task. Since the tractor had points and
condenser, and a 12 volt battery, I decided to convert the ignition
system to a coil system like that found on cars. At least, on older
cars, before everything became electronic on them. I already had an
auto ignition coil, so this conversion would require no expenditure of
cash. (It helps to be a junk collector!)

I first examined the existing wiring to determine how to proceed. The
points ground the system when closed, so the coil would have to go
"upstream" of the points. I disconnected all wires leading to the
magneto. I removed the wires from the key-operated ignition switch,
which now would have no function. Its only function was to kill the
engine by grounding the ignition when off. The tractor does have
electric start, but the start button is independent of the ignition
switch.

I connected the new wiring as follows: beginning at the positive
terminal of the battery, to which a wire would be attached with a large
alligator clip; to a 10 ohm (approx) wirewound resistor; to the positive
terminal of the primary side of the ignition coil; from the negative
terminal of the primary side of the ignition coil to the points, which
are connected in parallel with the condenser. When the points close the
circuit is completed. For the secondary side of the ignition coil: I
grounded the body of the coil by connecting a large hose clamp around it
with a wire inside. This wire ran to the tractor chassis. I used an
old, but still serviceable spark plug wire from a car to connect the
high voltage terminal of the coil to the spark plug. (Did I mention
that it helps to be a junk collector?)

The only place I could mount the coil was in front of the tractor grill
with wire ties. The wiring needed to be carefully routed to avoid
moving parts. I color coded the wires, red from the battery's positive
terminal, black from the coil to the points.

The system works very well. To start the tractor I connect the
alligator clip to the battery's plus terminal. (I have to take the hood
off to run it). I then set the speed control and hit the start button.
(This is after I have sprayed starting fluid into the air intake, as
that is the only way to assure a fast and reliable start anymore.) To
kill the engine I simply disconnect the alligator clip from the battery.