This happens to be a 1970 Triumph Spitfire but this system was used for a very long time on points ignition systems in all parts of the world.
It is most of the time just one wire from the R on the starter/solenoid to the "hot" side of the ballast resistor or coil like I did and my coil is 3Ω's and not the 1.5Ω's withe 1.5Ω ballast resistor.
Overall it just makes a 6 volt points system a 12 volt points system only in the start position.