I have no experience with an MB instrument cluster yet (knock on wood), but I assume there is a very thin printed circuit board on the back side. I knock out some of the instrument lights on an '89 Volvo by damaging this. Didn't have the tools or experience to re-solder the cracked circuit so I bought another instrument panel from a salvage yard, popped it in and all lights worked However, the 'new' odomoter had showed mileage.
regards,
Mark