Ignition System - MOTORCRAFT TFI-IV: Operation
The Hall Effect switch assembly consist of a Hall Effect device on one side and a magnet on the other. The rotary cup, which has windows and vanes, rotates on the distributor shaft and passes through the space between the Hall Effect device and magnet.
When a window is between Hall Effect device and magnet, the magnetic circuit is incomplete and no ignition signal (voltage) is created. When a vane passes between the Hall Effect device and the magnet, magnetic lines of flux are created and a voltage signal is produced.
When the vane clears the Hall Effect device and magnet, the magnetic circuit is once again incomplete and the ignition signal is turned off. These voltage on/off pulses are used by the EEC-IV system for sensing crankshaft position and computing desired spark advance.