I own a 2000 Mercedes S500.
The car will start intermittently, when it won’t start, it has gas and the battery power is strong. It will try to turn over but, will not complete task (fuel (choke) or spark issue). When the covers on the fuse boxes (left and right) are removed and fuses pushed on, the vehicle will start. It is unknown how long it will run after it starts (sometimes for 3 hours or more – at idle or sometimes 10 minutes or longer while driving). It appears to something with the fuses or relays but, not sure which one or ones cause the issue. This maybe a red herring but, also the front center control activation and indication buttons above the navigation system are non-operation (Hazard, door locks, rear headrest buttons, etc.), may also be fuse related.

 

you might have water in the water collector box under the hood. the drain gets clogged and then water spills into the car and runs back to the rear fuse box under the passenger rear seat, and shorts out the fuel pump relay. id check for water first in the water collector/ cowl. this is under the hood on the passenger side. look in there and there should be NO water. use a long thin rod or hanger to clean out the drain. all the way at the bottom just jam the debris down into the drain. this could be your problem. ive hundereds of these cars with this problem and various different symptoms because of it. you could have problems with you climate control blower motor since the water is running down onto it. wet carpets and mildew odors.