Fuel gauge reads past full all the time

power goes through the gauge down to the sender unit ,through the resistance to ground
what you have indicates a short in the wire after the gauge and before the sender unit

Here are some suggestions:

TROUBLESHOOTING PROBLEM: The fuel gauge does not work at all...no needle movement. With the ignition switch on, remove the wire from the fuel tank sending unit and ground it to the unit housing. This removes the resistance supplied by the sending unit, and should cause the gauge to swing over to the 'Full' position. Does this happen?
Yes
No
The gauge and wiring are good. The problem is most likely with the sending unit. The sending unit must be removed for further testing. (1) Ground the sending unit wiring to a good chassis ground (instead of the sending unit housing) and watch the gauge. Does it now peg out to the 'Full' side? Yes
No
The problem is with the sending unit ground. Either the unit itself is bad or the float/arm is binding/missing. The sending unit must be removed for further testing. The power supply to the gauge has been interrupted, (check fuses), the gauge is defective, or the wire from the gauge to the sending unit is open or has a break in it. Testing the Sending Unit After the sending unit has been removed from the tank, check to make sure the float is present, intact and still floats and that there is no binding with the float arm. Reconnect the gauge wiring to the unit and ground the unit. Move the float arm up and down. If the gauge reads full in the full up position and empty in the full down position, then the sending unit is good. Verify by hooking up an ohmmeter to it and making sure it reads 8-12 ohms full and 70-73 ohms empty. If not, the sending unit needs repaired or replaced. You can easily disassemble the head of the sending unit to clean and/or repair.

You probably have a ground wire not making contact to ground on the front tank sending unit. OR the sending unit itself inside the tank is faulty. Either way, when a gas guage goes to full all the time (empty or full), this indicates that NO ground is available for the sending unit.

I would bet the sending unit is bad but lets check it, a good test i use is that i have a used sending unit i connect to wiring to test the gauge and wiring, if the gauge moves when i move the testing unit then i know the gauge is good and the wiring to, locte the connector at fuel tank, and unplug it, this will be the one the leads to top of the tank and the connector will be on the side be the frame on drivers side, the way you know you have the right connector will be the truck will not run as this connector has the sending unit and pump wires in it, if the gauge goes to full then you know the wiring is good and the gauge is good, you can jump the two wires and gauge should go to full also. the problem is you must get the right wires for sending unit or you may pop fuse, let me see if i can get you a wiring diagram or just do the full test by unplugging connector.

Okay, your sending unit has a yellow and white wire, thats the sending unit wire, the other is a ground and we wont worry about that. so if you want to see if gauge will go to empty or full just unplug connector and gauge will move to full then if you take a wire and jump the yellow wire with white stripe to a good ground the gauge will go to empty, the thing is your gauge is on empty so sending unit may be grounded out, good day

I can only think of two possibilities:
1) The Ground Wire (goes from the sending unit in the fuel tank to the frame of the car) is not getting a good connection or
2) The fuel gauge in the dashboard is bad.

If your description means that the change in the gas gauge is random then check the ground wire. If you have a volt-ohm meter, try checking the resistance from the wire where it attaches to the sending unit, negative side. Remove wire from sending unit first. Make sure negative wire on V_O meter is connected to frame of car. Reading should be almost zero. Anything else and the wire you are testing does not have a good connection.
If your description means that you turn the car on and the gas gauge is reading full for awhile and then goes to empty, the gas gauge is bad.

I don't have the specs on your dash gauge. You would want to run an OHMmeter to test resistence at the dash gauge, then check the Ohms at the wiring from the fuel sending unit. The change in the Ohms from the fuel tank is what moves the dash gauge.

Best I can help with is a chassis diagram at Autozone.com, FREE, when you register your car.

You can go to a Salvage yard with an Ohmmeter and test a fuel gauge on-the-car to see if it has different resistance. This would indicate whether your gauge is good or not.

float may be stuck up;Take tank unit out and check it with power on and observe the travel and relative gauge position.

Ensure that all of the wire connections are clean, secure and corrosion-free.

2 Check your fuel gauge fuse if the gauge's indicator stays on empty when your turn on the ignition. If the fuse is good, join the sending unit connector to ground. Replace the sending unit if the gauge indictor moves to the full line.

3 Ground the terminal located on the back of the fuel gauge with a jumper wire if the indicator doesn't move. If it does move, consider replacing the wire between the fuel gauge and the sending unit. A poor ground is frequently responsible for fuel gauge problems.

4 Release the wire that connects to the fuel tank's sending unit. Confirm that there's no worn insulation that would permit wire contact to the body or frame. A fuel gauge reading of full generally indicates a problem with the tank unit, not the wiring.

If you ground the wire from the gauge to the sender with the ignition on the gauge should go past full. If it doesn't you'll have to trace that circuit all the way back to the gauge. If that circuit is OK you may have a bad gauge or no power to it. If the gauge does go past full when you ground the fuel gauge wire your sending unit may not be grounded. I'm assuming there is a float on the sending unit.

Dont we wish it be full all the time but gas in it. Okay for the sending unit reading full its getting a full ground reading,Key on engine off. does it move and goe down. It should if it doesnt the problems with the gauge itself. 2 test disconnect the wire harness, did the gauge go down. the problem will be in the sending unit can be a hung float(Rare).