what is my next step to troubleshoot getting fuel to fuel pump? on 2000 Mercedes-Benz S500

after replacing the relays under backseat again bc there was water in the relay boxes again, (don't know why), now the fuel is not getting to the engine. The fuel pump relay does work and so does the fuel pump. What would I troubleshoot next.

Asked by for the 2000 Mercedes-Benz S500