12 Volt Ignition Conversion For Simplicity 725
by Ken Williams
Click for a closer view
This covers the conversion of my 1963 Simplicity 725 to a
12-volt ignition system. Thanks to the numerous posters on this site who helped
me with this information, especially RobS and his instructions.
Reason for conversion - When I got my 725 the spark
plug lead was so old it was cracked and brittle. I found it would short to the
metal parts of the tractor and had to put a piece of plastic sleeve on it so I
wouldn’t loose the spark before it got to the plug. A coil change was needed.
I found there were four things I could do.
- Replace the coil
with a new one from Briggs. This would require removing the flywheel
and drive shaft plus make or buy a flywheel puller.
- Install an
electronic ignition. You can get a universal ignition module that
replaces the points and condenser. Jack’s has them for $13.50 and they are
part number 440-065. If you have points problems or a problem with a worn
points plunger this can work as a solution. It however uses the standard coil
in the flywheel so if you have a coil problem as I did this may not be the
solution. Note, you cannot use this electronic ignition with an external
- Magnetron ignition.
This is a replacement for the coil that may require repolarizing the
flywheel. I believe Briggs does this for free? It still requires the
flywheel to come off but apparently works really well when properly done. I
have not done this but have heard good things about it.
- Convert to a 12v
coil. This is really simple and, for me, was the best option. It
does not require the removal of the flywheel and gives the engine a solid hot
spark even in the winter. The downsides include it is not original if you
want the tractor to be pure and if the flywheel key shears you will not know
it until it is too late.
Click for a closer view
|Parts - You can get the parts from a
car junkyard or even stuff you may have laying around. I chose to go to
Jack’s Small Engine on the net and order parts.
- A coil with an
internal resistor. I ordered a Kohler coil from Jacks, part # 460048,
$25.50 and it included the mounting bracket.
- 12v condenser, again
from Jack’s, #455147, $3.85.
- Spark plug wire to go
from the coil to the plug. The inside of the plug wire must be copper,
not graphite as is found in car wires. I bought this from Jack’s #135178,
$11.90. It came with 2 connectors, a 90 degree and a straight. You
choose which one you need depending on how you run the wire.
- #14 stranded wire
- A universal ignition
switch. I got one from Trak auto for $4.99. You could just use a plain
switch but I wanted a key switch so it looked like the one I was taking
The Condenser - Remove the cover to the points. Take
out the old condenser. Also remove the secondary wire from the coil (it is
usually shielded by a small metal cable). This is from the coil inside the
flywheel and will no longer be used. I taped the end and folded it back under
the engine out of the way. Leave the cover off. Also remove the black wire
that hooked up to the old ignition switch and whose purpose was to ground the
points to shut off the tractor when the ignition key was turned to off.
I mounted the condenser in the same spot and even used the
bracket that came with it but I did need to trim the bracket for a perfect fit.
Leave the cover off for the “running the wires” section.
Mounting the coil - The coil should be close to the
plug so the plug (primary) wire is not too long. I mounted mine on the top tube
frame just under the hood behind the grill.
Click each picture for a closer view
|Here is a picture of my frame before the coil
is mounted. I did need to drill two holes into the frame for the coil
|Here is the coil after it was mounted.
The Ignition switch - The old switch on the tractor was
a grounded switch and had only one terminal, one wire to the points that would
short out the points to ground when turned off. Using this on your 12v set up
would drain the battery so a new non grounded ignition switch was installed.
The universal one fit right into the same hole as the old switch and looked like
an original. The new switch had 3 terminals, battery, ignition and accessory.
I did not use the accessory terminal.
Running the wires - Now that everything was in place it
was time to run the wires. I used #14 copper stranded.
- Run a wire from the
“battery” terminal on the new switch to the battery but don’t actually connect
it to the battery yet until all the wires are run so you aren’t running a hot
- Run a wire from the
“ignition” terminal on the new ignition switch to the “+” terminal on the
coil. I used crimp on eyelets to make the connections and I soldered them as
- Run a wire from the “-“
terminal on the coil to the points. This is connected to the same terminal
the condenser is connected to. Be careful you do not change the gap while
doing this or you will need to regap the points. Also be careful none of the
wires are grounding out. To fit the points cover back on you will need to
grind a small V or hole where the new wire runs in. Once the new cover is on
it is a good idea to seal this hole with flexible gasket so oil doesn’t get in
and gunk up the points. As long as I had the points cover off anyway I ran a
sliver if paper between the closed points to remove any oil mist on the points
- Hook up the hot lead from
the battery to the “battery” terminal on the ignition switch.
Spark plug wire - I removed the old plug wire and
installed the new one. The new one I got from Jack’s it had two tips that could
connect to the plug. One was straight and the other had a 90 degree
connection. I used the 90 degree connector after trimming the wire to length.
I used the excess straight connector to wrap the old plug wire tip, the one
coming from the coil in the flywheel. I then thoroughly wound electrical tape
around it and tucked it under the engine.
Testing and Adjustments - OK turn the key on and hit
the starter button to see how it works. I don’t believe you always need
additional adjustments but I did.
- I had to readjust my low
speed set screw. Perhaps it was due to a better spark at low speed.
- I also readjusted my
points. I did this while running. This is a sure and positive way to adjust
Good luck….hope this helps!
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