all fuel pump relays send the same amount of power to the pump i would replace the relay or check the wiring for shorts the inerta switch is the only relay (switch) inside the car besides fuses & other relays
did you do a compression test in the cylinders you might have a bent valve which could cause your fuel pump to over work something else you can try is lucas oil fuel treatment that stuff works
sometimes you can use a rubbermallet hammer tap on the gas tank as well as if the relay may have a problem if you triggered the inerta swith then it one of the other things you can try
do you still need a rear end out of a 65 mustang
i have a 1965 ford mustang coupe with 9" rear end with drum brakes looking for lincoln rear with rotors willing to trade if still needed