How do you tell if fuel pump or fuel pump relay --1993 Audi 90CS?

To determine if the issue lies with the fuel pump or the fuel pump relay in a 1993 Audi 90CS, start by checking for power at the fuel pump while the ignition is on. If there’s no power, the relay may be faulty; you can test the relay by swapping it with a similar one in the fuse box. If power is present but the pump isn't working, the fuel pump itself might be the problem. Additionally, listen for a humming sound from the fuel pump when the ignition is turned on, indicating it's functioning.