Hopefully someone will offer a better explanation, but FWIW, try to look at this problem from a simpler perspective. A breaker points ignition is actually very simple and has only a few parts, but it is essential to know how the circuit is supposed to be put together to do systematic and rational trouble shooting.
There are only 4 parts and a power supply. The 4 parts are the spark plug, the coil, a set of points and a capacitor (condensor - same thing).
It is easier if you think of there being two separate circuits. One circuit is just the coil and the spark plug. That is all that is involved in the high voltage circuit that creates a spark at the plug. The other circuit is 12 volts. (often it is less, but ignore that for now as it does not matter at all) The 12 volt circuit is made up of the power source, the coil, the points, and the condenser. Plus 12V goes to the positive terminal on the coil. The negative terminal is directly connected to the insulated side of the points. The un-insulated side of the points is connected to ground where the circuit is completed assuming the +12v going to the coil is a battery and the negative terminal on the battery is connected to ground as well. That is the entire circuit except for the condenser, which is an additional parallel circuit attached also (just like the coil) to the insulated half of the points and ground.
When the points are open, there is no complete circuit so nothing is happening. But when the points are closed, the circuit is complete, and the coil is now connected to 12V. The coil is literally just a coil of wire encapsulated inside a housing. When the points are closed, nothing actually happens that we notice, but because the wire inside the coil is, well in a coil, a magnetic field is created which is a natural physics phenomenon and a consequence of the electricity running through the wire wound into a circular coil. The more circles, the greater the magnetic field. Inside the coil there is also another coil of wire with a great many more number of turns than the 12V windings. It is not connected in any way with the 12V circuit, but it is wound around the same center point, and therefore is centered up in the magnetic field created by that 12V. This coil of wire is connected to ground on one end, and to the spark plug on the other. If enough electricity flows through these windings, it will jump the gap at the spark plug completing the circuit back to ground, so you can look at the coil for this high voltage circuit as the power source for the circuit. Remember, this circuit only has the coil, the high voltage coil wire, the spark plug and the chassis (ground) for components. The 12V is not connected into this circuit.
No electricity is created in the High voltage windings just because the coil is connected to 12V. Those windings are just hanging out in the magnetic field generated by the 12V windings. Electricity only flows in the high voltage windings when the magnetic field changes, and this is how the coil works.
When the points cam comes around and opens the points, the 12V circuit powering the coil, and consequent magnetic field suddenly stops. The sudden change in the magnetic field is what induces an electric current in the high voltage windings in the coil. If the change in magnetic field is very fast, and there are enough windings in the coil, enough voltage will be induced in the high voltage side of the coil to jump the gap at the plug making a spark and igniting the fuel.
In other words, when you open the points, the plug fires.
This actually has to happen quite abruptly, or the decay of the magnetic field will be slow and there will not be a quick enough change in magnetic field and no spark. That is what the condenser is for. It helps reduce a spark from occurring between the point faces and causing the break in the circuit to be too gradual (and also eroding the points).
The upshot of this long winded explanation is that you must have 12V at the positive terminal of the coil, and the negative side mst ground through the points, and "un-ground" when the points are open.
Check that you have 12V at the coils positive terminal. Rotate the engine so the points for that coil are closed. Manually open the points (by hand). You should get a spark at the plug when you break the circuit when the points open. Take a new plug and plug the high tension lead from the coil you are checking into it. Make sure the threads of the plug are firmly touching ground (remember that complete circuit!). If you don't get a spark, unplug the negative side of the coil and see that the circuit opens and closes with an ohm meter, or simply take a grounded jumper wire and imitate the points by using it in place of the negative wire going from the coil to the points. Connect it to the negative terminal. When you remove it suddenly, you should get a spark at the plug.
