The relay is internal to the IPDM, which is under a cover in the left rear of your engine box. You need to remove the front intake duct to access it (2 pushclips and a 6mm screw). As shown in the link, you're looking for a white wire on pin 76. The fuel pump fuse is also in the IP, the label inside the cover will identify it. The relay is "downstream" from the fuse, so if the fuse and relay are good, the wire should go hot with a test light for ~1-1/2 seconds when the ignition is turned on with the engine off, or on constantly when cranking. If the fuse is good but you have no output, the IP has to be replaced (the relay is not serviceable). If you have juice there, then the problem is not the relay. The most common issues with Nissan pumps are intermittent sticking (usually means the pump motor is dying) or a corroded ground terminal on the pump connector. The pump will be under the righthand rear seat beneath a service cover. If you hammer-whack the outside of the tank and the pump starts, replace the pump. If it won't spin, then pull the seat and check the connector. The ground contacts sometime corrode so badly they blacken. This is usually from excess startup draw from a dying pump motor, so if you find it, replace the pump as well as repairing the connector.