If you look at the wiring diagram, the pints earth the coils which have a red/white positive feed via the ignition switch.
ther is also a condesor to prevent sparks across the points, preventing arcing (sparks) which will erode the contact surface.
the time the contacts are closed it powers up the coils in primary coil and when the contacts separate, the built up power in the coils has no where to go so passes to the secondary coils and jumps the spark plug gap (the easiest earth path). thats why HT leads are well insulated, stopping any earth leakage. hope that sinmplified explanation helps.