Pick-Up Coil: Description and Operation

Igniter, Signal Rotor, and Air Gap Overview:

The Electronic Ignition System uses an igniter assembly (mounted in the distributor) in conjunction with the vacuum advance unit, to control the ignition timing under all engine conditions.
The igniter coil generates a voltage signal when it's magnetic field changes as the reluctor (signal generator) passes the igniters air gap. The low voltage signals are used by the Igniter unit to switch the ground circuit to the coil on and off, controlling firing time of the spark plugs.