Locating fuel pump wiring diagram for a 2005 1500 Ram. The fuel gage in pegged on empty.

It's probably the float on the fuel pump.pull the pump and clean or just replace the fuel pump and float.

the sensor is on the fuel pump in the gas tank

Am working on the same problem. Have narrowed it down to a couple of things. The primer curcuit on my '88 is not work off the computer it will not prime the fuel system. Have found away around that by putting in a new relay off the starter line. The main problem though is that the check valve in the fuel pump is shot and allows all the fuel to drain back into the tank. It takes too much time to get the fuel preasure up if the fuel system is completely empty. Am going to replace the fuel pump and see what happens. The fuel pump relay is located under the glove box, have not found diagram map of the relays there, there are 10 there. If you need a wiring diagram for your car, go to autozone, can print off a wiring diagram there. Good luck.

You have lost the ground input to the gas gage. Its the black wire coming from the fuel pump connector at the fuel pump. Either the wire is broken or the input to the body control computer is broken, thus creating high Resistance on the input wire. The computer will think the tank is full, a shorted wire would indicate lo Resistance and read empty. Locate the fuel pump connector and jumper the black wire directly to the body (ground) and turn the key to run, check gage. If reads normal the wire is broken betwwen fuel tank and its ground location.

The Fuel SENDING UNIT HAS FAILED And IS CAUSING This Fluxuation Of the GAGE, The Sending Unit Is Located IN the FUEL TANK & Requires TANK REMOVAL to Replace it,
NOTE;;;; IF YOU HAVE HAD THE FUEL PUMP REPLACED RECENTLY, THEN 99% PROBABILITY THAT THE INSTALLER WAS NOT VERY GENTEL WITH IT, THIS IS A COMMON REASON FOR THIS TYPE OF FAILURE.

Gauge is not connected to any relay,its a signal from the fuel pump sending unit, you do not get voltage from that wire for the sensor you need to use a multimeter and test for ohms, every manufature is different and cant recall what it should be empty or full.

Get a shop manual or even call the local repair shop/dealer and they might give you the information you are looking for, but sounds like you have a bad sending unit and need to replace it as an Assembly.

Testing the fuel gage requires accessing the harness from the fuel pump and grounding the yellow / white wire with 160 ohms resistance this should cause the gage to read full, and with the circuit open you should have the gage reading empty. If the gage works in this order then the likely failure is the sending unit in the tank , and will require replacement.

Have you checked the fuel pump relay under the hood and the fuel pump fuse in the dash?It can't hurt to rule those out first,right?
The fuse and relat diagrams , should be in the owners manual.
Good luck.

Sounds like the fuel sending unit is bad, which is in the gas tank, along with the fuel pump.

Jason, as far as the fuel gage, try a couple of resisters at the wiring for fuel gage sending unit, in gas tank. It's two wires, use the resister inline between the two wires. One resister is for low fuel level, the other for high fuel, If the gage reacts properly to both resisters, the problem is the sending unit in the gas tank. You can try 40 ohm and 250 ohm resistors. I used to get resistors from radio shack, I don't know if they went bankrupt? The store in my community closed. Other places may have resisters?
Just to add, the wire colors for sending unit/sensor are purple and black with white tracer.