Interior Lamp
WARNING: This page is about a different car, the 2018 Ford Focus. However, it is still accessible from the selected car via links, so may be relevant.
All of the interior lamps receive voltage from the interior lamp relay (integrated into the BCM) when the battery saver feature is not active. This is used by each interior lamp to power the LED within it.
The front interior lamp uses a private communication protocol to command the rear lamps on or off.