Fuel Guage below empty

[R32gtst1992]

So started off as it would randomly read empty then stopped working completely.

92 gtst 

Stock pump I'm assuming haven't pulled it out or done any diag yet

[joshuaho96]

Check the signal at the pump hat and see if it’s also indicating something broken. If it isn’t then you need to go upstream. I would probably check the signal at the gauge cluster at that point. 

[Duncan]

hopefully the tank is pretty empty....pull fuel pump fuse, crank until it does not run any more, remove fuel lines from fuel pump cradle lid, unplug pump and sender wire, take the lid off, check that the sender arm is connected properly to the cradle. If so, use a multimeter to check continuity between the sender scale and the plug on the top of the hat. If that is OK, pull the dash, find the wire for fuel level and check it has continuity with the wire that plugs to the top of the cradle

[BK]

Ok to be less vague and before you do anything above, first thing is to pull the 3 pin sender signal plug from the fuel tank tophat. (The 2 pin one is your fuel pump power)

Get a multimeter

Test resistance between the 2 outside pins on the 3 pin connector on top hat, this is the level sender for gauge. (Middle pin is low fuel light, not relevant to gauge)

Normal resistance is around 4 - 6ohm for full and 80 - 90ohm for empty.

If resistance is higher than this, like in the k ohm or just open, the problem is inside the tank on the level float wiring / contacts. If you have resistance in this 5 - 90ohm range problem is on upstream wiring towards or at your gauge end.

Most likely it'll be in your tank (fixed this lots), especially since your gauge is way below the empty scale it indicates an open circuit.