To expand a little on what Hotrod said. Capacitors are not shunts. Their construction simply put, are two conductors, like small sheets of aluminum, separated by a sheet of insulation or dielectric. So they do not conduct current as a shunt would. A failed capacitor is, but not always a breakdown of the dielectric allowing current to pass through it. Simply put, they absorb the arc voltage with the points open, then discharge said voltage when the point close.
One of the hardest things for me to understand when in school was, “capacitors block de voltage but pass ac voltage.
