1995 GMC Truck fuel pump relay

Welcome to the forum, basic relay, terminals 85 and 86, one is voltage the other is ground for coil side of relay. Doesn't matter which is which, as long as there is no diode in the circuit. Terminals 30 and 87 are for the load/switch side of relay, the switch side is normally open untill there is voltage and ground on the coil side, then the switch closes, continuity from 30 to 87. Your relay terminals may not be numbered like that, but same principle. The relay diagram below came from the 12volt.com. Basic relay. Also, if there is an oil pressure switch in the fuel pump circuit and the circuit is functioning properly, the pump will run without the relay, once you crank it enough to bring up oil pressure and the switch closes, provided there is voltage to the switch.