This harness is used in the instance you want the fuel pump to turn on and run when the car is in the "key on" mode. This will allow you to drain the tank if you are switching fuel types. Simply unplug your harness from your fuel pump driver module and plug this in. Then when the vehicle is "keyed on'' it will run the fuel pump.
2011-2014 Mustangs have the Fuel Pump Driver Modue (FPDM) located in the spare tire well. 2015+ Mustangs have the FPDM located under the rear seat on the driver's side of the vehicle.
2011-2014 Mustangs have the Fuel Pump Driver Modue (FPDM) located in the spare tire well. 2015+ Mustangs have the FPDM located under the rear seat on the driver's side of the vehicle.