Part #001 542 96 19 says "Auxiliary Fan, Stage II Relay".
I'm interested in the answer to the Fuel Pump Relay question too -- I have a '92 300E with the identical problem and can't find that relay??
I've replaced the fuel filter (didn't fix) and will be replacing the OVP relay to see if that helps.
My OVP relay is to the rear of the battery, under the plastic protective flap, my guess is yours is too.
1999 E320 Wagon