When my '86 300E failed to start, it was the fuel pump relay. I had someone listen back by the fuel pumps when I turned on the ignition. They could not hear the pumps. I then pulled the relay and jumpered the pins on the relay socket to turn on the pump. The pump ran so I concluded the fault was the relay.

I opened up the relay and found a burned trace on the printed circuit as well as some bad solder joints. I resoldered the relay and put it back in while I waited for a new one to arrive. I keep the repaired relay in the trunk just in case.

__________________
1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog