Hi hope you can help. Tried working through this swapping out known good parts from my old vehicle same year and type!
The Fault:
Instrument lights illuminate but when you switch the lights on they slowly dim down and start to flicker.
Action taken:
Isolate battery. Replace Lighting switch and LCM for known good one.
Checked to see if it had cured the problem before reassembling dash board and trim, it Worked as it should without any flickering.
Disconnected Battery. And reassembled trim. Reconnected battery and started car and did the lock to lock to reset.
Tried Lights. Sides and Headlights. They worked fine but instrument back lights were back to rapid flickering when turned up to full brightness. But when dimmed down to barley visible the flickering stops.
I have tried PM ing the chaps that have had this problem in the past but nobody has responded.
So I decided to consult the Oracle
2003 L322 4.4 LPG and Android header unit. Poorly fitted by previous owner.  Eddie the eagle watch out 👀