Have you been in any type of a wreck? If so the inertia switch is located in the circuit between the fuel pump relay and the electric fuel pump(s). If you have been in a significant impact the mechanism inside the switch will cause the switch to open the electrical circuit, shutting off power to the fuel pump as a safety precaution. The inertia switch is in the cab on drivers side, up against the firewall, to the left of the brake pedal or behind the right kick panel. I would suggest buying a new one because it is not something you can reset.