The central locking pump is one of those overengineered but cheaply built components Mercedes is known for. It lies in a sump in the bottom of the boot and if there are any leaks it fills with water and fails.

If the pump fails your locks don't work and your security system goes bananas. Park lamps may go on and stay on. Interior lights may not work.
Easy repair and you can find them on E-bay for about $250 most of the time.

I sealed mine up in aplastic bag and pulled the black rubber stopper out of the sump. No more issues.