Check/replace the micro-switch in the liftgate. Should be a DIY under the "Articles" section.
The light problems are usually caused be faulty bulb housings. Try a "Search" as there are plenty of fixes.
GL.

__________________
Sent via Telegraph Wires using my Morse Key.
2021 X5 xDrive40i
2015 X5 xDrive35i MSport
(Traded) 2013 X5 xDrive35i