The unit features 2 rotating windows with 3 faces each and rotated by the action of 2 solenoids.
When unpowered or no autoland announciation is active the black face is shown.
The upper window shows LAND 2 or LAND 3 on green background to show when Autoland is activated.
The bottom window shows NO LAND 3 or NO AUTOLAND on orange background when for any reason the autoland in selected category can't be accomplished by Aircraft systems.
Here it is the pinout connection diagram for each unit:
As you can see the unit has 2 x 28VDC power sources, one provided by Aircraft battery and one by the left DC bus for the captain and from right DC bus for the first officer.
The announciators outputs are GND with reference to the 28vdc supply.
And here you can see a video of the unit in self test mode.