I have a 1984 Camper on a Ford F350 Chassis w/460 V8
My Battery has been going dead lately, I found that when the key is off I can hear a humming sound from the Rear gas tank.
Anyone Know what may be causing this, It does have an electric fuel pump.

Thanks,

 

Most of the time a relay that has the contacts welded together will stay energized.
If you have the owner's manual, it should indicate which relay is the fuel pump relay and will also provide it's location.