not sure if it helps. I have a 2000 W220 and all lights on the entire instrument cluster went out. The speedo, oil, petrol, ....... still works but just no light. I think the CLK has a similar cluster where there is a BIG LCD on the cluster.
What I notice is that if I drive with the door open, not too slow but not too fast, all lights came back online and the LCD had huge warning regarding door not closed. But as soon as the car stop, everything back to normal, i.e. no lights.
This prove to me it is not the fuse but must be the motherboard. Of course the dealer say "replace it". I just had to convince myself before spending the $$$$ to get it replace at the dealer. I had to get it done by the dealer as all the information is stored in the cluster and must be transfer to the new cluster.
This process can only be done by them as I was told!