The issue is with the gearator in the pump motor block.The seals inside will go bad after time and allow fuel to pass and will blow the fuse out of the line quickly after the pump is trying to run at full draw.On a FASS or AD all you need to do is to look the T-Blocks over well at the weep hole and if the pump is wet or dripping the pump motor is bad and needs replaced.Simple fix,just time consuming if you have it warrantied as you will have to send the pump motor T-Block back and they will warranty it for the original owner,providing the proper warranty paperwork was filed.In My case,I have one pump from each Manufacturer and carry a spare pump T-Block here at home for each to minimize down time.My 200gph FASS has been perfect for now almost 6 years and My AD has never been replaced since 2010.
Also note ALWAYS run your aftermarket fuel systems through a external electrical regulator that handles the heavy electrical draw and use your key on position or a separate toggle switch to turn the pump on and off manually.I run mine so the fuel system can be stopped By Me on a lighted rocker switch as if something goes wrong I want control of shutting down the fuel source.