I have a 1999 E320,went to start today, no solenoid click, no starter action,lights on dash work ,headlights go on,can here fuel pump cycle,although i did notice the right tail light on when exiting the car,i think this is some sort of indicator?Battery new last year and put on a jump pack just to make sure.

 

For some reason nobody had any solutions,well after Itested the battery, the next place was to check the fuses which were good.Next I went to the starter relay,and there was the culprit,a bad relay,so I called mercedes for a new relay (which is made in portugal by the way) and they wanted $75, for $6 relayI crossed at NAPA.Hope this helps someone out there.

 

The k40 relay module can be a culprit. It supplies power to the me-sfi control unit and will cause intermittant problems such as a no crank or no start , often temperature dependent.