Current generation of Automatic and Automatic+ system use 2 magnet encoder rings to provide the speed signals. Both the rings are required for correct system functionality and without these the system will not shift.
The Input Speed Shield (part nr. AUT-ISS-OE) provides us with a signal for input speed and is mounted on the sprocket retaining ring as shown below:
The Output Speed Encoder (part nr. AUT-OSS-OE) provides us with a signal for output speed and is mounted on the hub and secured with a small screw at 1 Nm magnets facing the flange.
Older Harmony system used only one magnet disc (in black or silver), and used the sprocket itself for input speed. If changing from the old Harmony system to the latest, you must remove the old magnet disc before assembly of the new parts.