At the fuel pump relay, terminal 30/51 is receiving current from the fuse. Check the fuse. On my 164 its located in the 3 fuse auxiliary fuse box on drivers side of the engine compartment. Connect a test lamp to 30/51 and ground. If fuse is good, current will be received. I dont remember if it is always hot or the ignition must be in the run position. Try it both ways. Terminal 87 is sending curent from the relay to the fuel pump. Connect a test lamp to 87 and ground, turn key to run position and test lamp should come on for 1-2 seconds......IF, the main relay is activating the fuel pump relay. The main relay does this by completing the circuit to terminals 85 and 86 on the fuel pump relay. If everything checks out, the relays are working properly. You can then check the fuel pump directly, by connecting a jumper from the fuel pump wire(which was connected to terminal 87 on the fuel pump relay) and + on the battery. For safety I like to use a 12V DC model train transformer for this kind of stuff rather than the battery. If the pump is good, it will run when you complete the circuit. For safety, if you run the jumper from + on the battery, you may want to run the jumper through a momentary contact switch.

Some time back, I had a similar situation where everything seemed to check out in the driveway but then, after driving for a while, the engine would suddenly die.......and the fuel pump wouldnt run. Turned out to be an intermittent problem in the relay. I replaced both fuel pump and main relays. Problem solved.