you have a bad ground on the battery or on the engine clean all the grounds and the positive connections, this is a com mom problem. with an ohm meter check to see if you have more than .2 ohms Resistance and you will have found your problem. also battery cable could be corroded so check...
First before you change the fuel pump how do you know it's the fuel pump? and if you don't know then you need tofind out what your problem is, when you turn on the engine and you hear a pump running in the tank then the pump is working change the filter and try starting the car. If the pup rums...