Where is the fuel pressure release valve on a 2004 ford mustang?

If you're talking about the inertia switch that is located in the trunk under the cardboard mat, if you switch that and turn your car on until it dies from running out of fuel it will depressurize the fuel lines, If you're talking about the pressure release valve on the fuel filter then that is located on the fuel filter itself and I would suggest wrapping a towel or something around the screwdriver or whatever tool you use to push the pin (it's like the valve stem on tires, if you don't know what those are then just take your car to the dealership to have them change your filter for you) because gas is still going to spray out of it because it's pressurized in the filter itself. Hope this helps