I'm gonna say there's a problem with the system ground....undo the lug that connects to the chassis ground and wirebrush that lug...and the space where it bolts to, think that insufficient ground to the relay box has the relays dropping out....combined with a battery that may be older than five years old has led to a relay dropping out....the fuel pump or ignition relay is not seeing sufficient voltage to stay engaged....test at the relay box for GROUND...and varying voltages from the corrosion that is holding up the show~