Originally posted by Diablo
Actually, a changing magnetic field will generate current in a nearby wire. Guess how a generator works and an electric motor. There is also the high secondary voltage in the spark coil to worry about. When the high voltage collapses (when the plug fires), this generates a strong magnetic field radiating from the high tension wire. Ain't electricity and magnetism wonderful.
This is true but the generated current in the wire will be of very low frequency and will not cause trouble with the receiver. When the plug fires the spark creates a noise pulse that contains all frequencies. This is what causes trouble and must be shielded or suppressed.