Put new fuel pump now the pump runs but the power wire only has 7 volts of power how much is it suppose to have

It sounds like you have done some troubleshooting on your own and have determined that there is a problem with the power wire to the fuel pump. Running a new wire from the fuel pump power wire to the relay is a good solution if the original wire is damaged or burnt out.
Before connecting the new wire to the relay, it is a good idea to test the fuel pump by running a wire from the battery positive terminal to the fuel pump power wire. This will ensure that the fuel pump is working properly.
Once you have confirmed that the fuel pump is working, you can connect the new wire to the relay. It is important to connect the wire to the correct pin on the relay. In this case, you should connect it to pin 87, which is the power output pin.
It is also important to ensure that the wire is properly insulated and secured to prevent any electrical shorts or damage. Once the wire is connected, you can test the fuel pump by turning the key to the "on" position and listening for the fuel pump to engage.
If everything is working properly, the fuel pump should only receive power when the key is turned on, and the new wire to the relay will provide a reliable power source for the fuel pump.

There should be battery voltage at the fuel pump. Check the battery voltage at the fuel pump relay to be sure that there is power coming from the battery. Check voltage at fuel pump fuse.

I don't believe it has one. I've heard some pretty reliable sources say this safety switch is a Ford-only product. First check the fuel pump fuse. It's fuse #1 in the Power Distribution Center, a 20 amp fuse.

If the fuel pump in the tank is not turning on to put gas up to the engine, you have a problem in the pump circuit or a bad pump.
There's an easy way to determine which it is. You will need a voltmeter or at least a test light.
Find the gas tank electrical connector. It will be near the tank. A wire loom of about 4 wires will likely come from the top of the tank and run down to an electrical connector, probably close to the side frame rails. Pull the connector apart, and on the harness side (or chassis side, not the tank side of connector) identify the dark green with black stripe wire in the connector. This is the power wire to the fuel pump. You need to check if it has voltage on it when the pump is supposed to be running and pumping.
You will need a helper to turn the key to start and crank the engine over while you check for power with the voltmeter or test light. If the voltmeter says battery voltage-right around 12 volts, 11.8 volts or more- or if the test light comes on brightly, then you know the pump has failed (90% certainty) and you need to replace it.
If there is no voltage on the dark green/ black stripe wire with the engine cranking, it is not a pump problem. You will need to consult a wiring diagram to diagnose the fuel pump circuit. I just looked and there is no inertia switch.
Good luck.

What do you have coming out of the fuel pump relay ? The connector at the tank includes the ground wire for the gauge which is about 7 volts. Make sure you are checking the right wire.

If your power plant to the fuel pump has no power u can run a new 12 volt wire to the pump make sure it's hooked up as an accessory so it will shut off the pump when you turn off your car

The 7 volts tells you your dropping the other
5.6 volts somewhere

Check the entire circuit with the problem for
voltage drops to ground or poor grounding

Pretty much need a wiring diagram to even
start on it

first thing to check power at the plug at the pump itself if you have 12 volts there, make sure the ground wire has a good connection at the frame rail,if thats good the pump wire that runs thru the fuel pump hanger maybe broken

Disconnect your battery. Switch your meter to ohms. Don't let the battery terminals touch the metal body. Put the negitive meter lead on the body and the positive meter lead on the one that is only 3 volts at pump. There should be no continuity. If there is, then there might be a short.
Next try putting one meter lead on the 7 volt main connector and the other on the 3 volt supply side. There should be little resistance. If resistance is high then you might have a break in the ciuciut.

I hope this helps.

the other wire that is "dead" is the ground wire for the fuel pump. try cutting that wire after the connector towards the pump, and running it to a good clean ground.

a volt meter on the fuel pump fuse is the first. if its getting power there must check the pump its self. pretty sure3 nissan still puts theres in the trunk. if it is theres 7 bolts to undo on the cover plate. then you will see the top of the pump. check those wires with the volt meter