The fuel pump (as well as the fuel filter and accumulator) is located in an assembly behind the rear passenger tire. If you're going to do anything with any of the parts back there, I strongly urge you to go to your local MB dealership and order replacement hoses that run from the filter to pump and pump to accumulator *before* you do anything. It's a messy, uncomfortable job, and those hoses are old and brittle. As soon as you touch them they'll start to leak, and you'll wind up having to replace them anyway. Best to do the whole job at one time.
That means also order the fuel filter and, if you've been having hot start issues (the car starts fine when cold, but you have to crank it for several seconds when starting warm) replace the fuel accumulator as well. You can use a padded pair of vise grips to squeeze off the fuel line coming from the gas tank to keep your tank from draining when you disconnect the fuel filter.