Farmall tractors that were shipped with the lighting system preinstalled came with a standard distributor. The ones shiped with no electriocal system came with the Magneto ignition system that generates its own voltage without the need for a battery. It is spring loaded and winds up before each spark, Every time it sparks it will click which when the spark is generated. You need to make sure you oil and grease the magneto in the proper places. See the manual for more info.

Wiring:
See diagram for firing sequence, This should be marked on the block. Not shown is the kill switch wire that runs up to the switch at the seat. The magneto should never be connected to your electrical system. It generates its own voltage.

Troubleshooting:
Remove the unit and rotate the cam by hand clockwise. It should wind up and then click when it releases. This fast release forces the magnet inside through the wiring field creating a voltage. The voltage is routed to the points and the coil which break the voltage at the right time causing the coil to create an "inductive kick" creating the spark. You can test for a spark by holding the tower wire near the case. If the unit clicks but has no spark it could be a problem with the points or the coil. If the unit does not click or won't wind up it is a mechanical problem.

Conversion:
If you have a bad magneto. When you rotate the cam by hand it doesn't wind up and then release making a click and then a spark. You can add a auto coil and convert it to a 12 or 6 v ignition system. All you do is remove the wire from the tower and connect it to a coil. You then connect a wire from the kill switch to the ignition wire on the coil and the + wire on the coil to correct voltage.
If you do this conversion and no longer need the old coil please remember that others are in need of the coils to repair magnetos.

I suggest that you do not convert your system because it will work better on the magneto. Try to get it working. Many tractors have good magnetos but were converted for no good reason. In fact some mechanics used to convert every magneto they saw only because they did not understand them.

New timing page added click on image to view.

New update 2010 you can now get a kit to convert your A to electronic igniction.