The fuel pump and related components are protected by a large plastic shield under the car between the rear tires and offset to the right (passenger side).
The 1989 Mercedes Benz 300E came equipped in a 3.0L L6 engine. It has a canister type fuel filter which will be located underneath the car and forward of the fuel tank in the fuel line. The OE replacement fuel filter is Fram #G3737.
There are two fuel pumps in a Mercedes 300E
The fuel pump relay on a 1988 Mercedes-Benz 300E is located on the passenger side, near the firewall, by the battery. Mercedes-Benz was founded in 1926.
It's near the right rear tire.
Just in front of the right rear wheel.
Between the rear seat back and the trunk.
Near the right rear tire
Behind the right rear axle next to the fuel pump (under the car)
The relay is a black retangular box located between the battery and the firewall.
Right next to the fuel pump, not far from the fuel tank and the rear axle. I don't remember, but I think it may be located on the right side.
Attached to the fuel lines that come off the fuel distributor. Follow the lines towards the head. Hope this helps.
DexIII/Merc