Fuel pump will not shut off
Suspect the fuel pump relay. Normally the fuel pump relay operates during starting and when turning off the engine. If it is stuck, the pump could continue to run. A full explanation of how the relay works and how to check it is quite long. I suggest you check the net for info on how a fuel pump relay works and conduct the electrical test. It is straight forward. Basically, if the relay is sending power to the pump with the engine off, it is defective.
Fuel Relay contact stuck closed. Replace relay
Search Ford F-150 Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Ford F-150 Experts