Fried fuel pump relay
If you do fry your relay, remove it and short terminals 7 & 8 - that will make the pump run (but you will lose the rev limiter built in to the relay) and at least get you mobile. Just remember to pull the shorting wire when you leave the car.
If you short using an ammeter across 7 and 8, you can read the current consumed by the pumps - my 560SEL (1990) with one pump consumes 8 amps, which is correct. Two pumps should consume 15 amps. Anything much higher and you may have a pump ready to go out.