I just replaced the fuel pump on my mercedes.

I located mine on a 190E below the windshield, under the hood, on the passenger side, in board of the battery. There were 2 together in a relay center outboard of the fuel computer. One said KLIMA and the other said konstaadt or something on it. The f/p was behind the klima and the ovp was an aluminum tower shape with a red top containing a 10 amp atc fuse. Autohaus sells a kit for test jump which eliminates the relay during testing. Its cheap. And it took a day or two. But my chevy runs great when I go to the wrecking yard to find expensive german parts to try. For cheap.

Oh, the tests. I went to the public library and they offered a mitchell database. It included the test procedure, jumping the relay pins and gave illustrations. I also had a chance to consult bulletins and recalls info for my vehicle. The component locator was sorta vague and pics are a little ambiguous. Once I located the ovp relay, I just went to the two nearby. Printing a schematic came from a haynes manual they had. 10 cents a page for printing. Couldnt take the paper book out in the rain. DVOM and test light came from harbor freight tools. Relays, if found faulty, are repairable to a small extent but they are available on ebay for less than $35. Looking at the pics on there can help locate and identify the parts. Theres also mercedes info sheets called startekinfo. Ask the librarian. Or you can google it