1999 Mercedes SL500: While driving trunk lock will sometimes open and indicator light will come on. Now door lockssometimes open while driving and interior lights will come on. What could be the problem.

 

It is likely that it is the PSE control module in the boot. (Pneumatic / Security)
The interior lamp and the locks are controlled via this unit.
These give trouble if they are in a damp environment (condensation)

Get the dealer to scan the OBD (On BoardDiagnostics).
This will confirm my suggestion.0

Stuart