4AC wont start

[Ivan141]

Well all I can tell you is the basic principle that most simple ignition systems use. I'm just assuming it's not a breaker-system (with contact points). Usually there are 3 main components, the distributor, an igniter unit (small black box or whatever), and the coil.
The distributor contains a hall sensor that sends a signal to the igniter, which in turn makes the coil fire.
The coil has 2 low voltage terminals... 1 gets a constant (ignition switched)12V, the other is directly connected to the igniter unit. When the igniter switches it grounds the wire to the coil, causing a current peak in the coil, which then creates the high voltage that makes the spark happen (works like a transformator).

That's the basics you'll need to have a clue as to what you are doing... older systems with mechanical contacts (breakers) work a bit simpler, those have a little contact point inside the distributor which is controlled by a small cam. When the points make contact the coil is grounded and hey presto you have spark. If you have one of those it's worth checking the capacitor, since those can go bad once in a while.