From the wiring diagrams in the Haynes manual, I think I have figured out that the green wire is used to bypass the ballast resistor on the coil during cranking, whereas the black wire is connected to the solenoid.
In cars with breakerless ignition, which I think I have, the green wire is not used because there isn't a coil resistor.
Yes, you're right, there's no ballast resistor on cars with electronic ignition. If you have standard breakerless ignition, you should be able to tell easily. Just take the cap off the distributor, and have a look inside. If itís got points, itís not breakerless. If it is a breakerless ignition, then chances are that itís a Marelli or Bosch reluctor distributor. This has a toothed wheel with 4 teeth below the rotor button, or below the advance weights in the case of the Marelli distributor. To give you an idea of what the toothed wheel looks like, hereís one from a Mitsubishi Sigma, shown below.
You can see that just below the personís fingers, is the coil which picks up pulses whenever a tooth passes it. That should have one or two wires coming out of it, and going off to the electronic ignition module. One side is usually earthed, which is why sometimes they only have one wire coming out of the distributor. With the Marelli breakerless ignition, the ignition module is included with the ignition coil, in a large finned metal heatsink arrangement Ė it looks like this one, from an Alfasud, shown below. (It's a bit hard to see, because it's scanned from a photostat pic.)
They are generally relatively maintenance free Ė the only things that need attention are the distributor cap and rotor button, which eventually may need replacing, as with a points setup, and the advance weights, which occasionally need lubricating.