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The modules in the infotainment system in these vehicles are connected in a loop, fibre optic, called MOST.
If one of the modules in the loop fails to pass on the signal (for whatever reason) then the whole system goes offline.
In a 2008 L322 fully loaded that list of modules includes;
Head Unit
CD Changer
Touchscreen
TV Tuner
Rear Seat Entertainment module
Navigation DVD drive
Bluetooth phone module
Audio Amplifier
Any one of those offline can take out the whole system.
The method for testing is to bypass any modules which are optional, using a blanking loop
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You unplug a module and fit the blanking loop in it's place, which "restores" the loop if that module happens to be the one which was faulty.
Some modules you can't really bypass; the head unit, which is the master of the network, and the touchscreen. In which case you can only really substitute in another one for testing.
If you have a suitable diagnostic tool, the head unit (ACM, or FEM, depending on terminology) is on the MS-CAN network, and should communicate. If you have no comms with the head unit then that's possibly faulty. If you do have comms it should give you fault codes like "MOST loop interrupted / incomplete" and possibly listing specific modules in the MOST network that it is not communicating with.
With an L322 the most common things I've seen are the TV tuner failing, or other modules there in the left side of the boot getting wet. Very rarely is it any of the modules up front like the head unit, CD changer or touchscreen.
The blinking light on the left side knob is a sign that the MOST is offline.
There's one other thing, the head unit controls a relay which provides power to many of the other modules in the MOST loop, if that relay is not being activated then you'll have the same result as now. Strange enough I had one 2005 L322 where the wire to that relay was mysteriously broken somewhere between the dash & the fusebox in the boot, random...
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