Your car may have a MAS relay. Picture of it below. Back near firewall. Black knob turns and off it comes.

If you have this - fuel pump relay is within - pins 1 & 2


http://www.ebay.com/itm/Mercedes-OEM-MAS-Relay-Part-0075456532-/151355223684?pt=Motors_Car_Truck_Parts_Accessories&hash=item233d796e84&vxp=mtr


MAS diagram follows


http://www.peachparts.com/shopforum/attachments/tech-help/106582d1351097166-mas-relay-diagram-mas-relay.jpg


If car runs with pins 1 & 2 jumpered, you likely have found your problem.