1991 Ford 4x4 daul tank fuel problem

I have a 91 f-150 with daul tanks, pulled the codes came out with (87) primary fule pump circuit failure, changed the relay, checked voltage at the front tanks fuel pump 12V., checked inertia switch (not Tripped) still nothing when you attempt to start, no fuel pump noise that is on either tank. I am totally baffled on this one. Anyone have any ideas, would appreciate the help
:banghead: