1989 F250 Diesel twin fuel tanks fuel guage does not work

Check the supply voltage and connectoins between the guage and tank sender.

The wire to the sender in the fuel tank is shorted. If it was open or disconnected it would read full.

It could be the tank switch contacts on the drivers side frame, I think there are copper contacts inside.

wiring harness under dash.
wires coming off top of fuel tank.
check all fuses.
do you do a lot of off roading - you may have cut or pulled a wire out.
finally you may have:
1. a bad fuel tank sending unit - need to drop the tank to replace.
2. a bad fuel gage.
3. a bad instrument panel

A loose connection on the sending unit could cause the problem but also moisture in the tank in cold weather could also be a factor in which i would add fuel line antifreeze to a full tank of fuel..........Hope this helps you out.

try loosening the injector lines a little then crank it.it probably has air in the lines and wont blow through the injectors,once fuel comes out while cranking,tighten them,if this is the problem it should start but run rough untill the lines are tight,it shouldnt hurt much to get a little fuel on the engine

• Check the floater in the tank may be you need to replace it with a new one.
  

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2 things.
There is a sensor that goes from the dash to the fuel pump. If it is disconnected, dirty, or faulty, then thats an easy fix.
There is also a float in the gas tank itself. From what Ive been told after time, or going over big speed bumps, etc, that the float just simply doesnt float or register.
Mine actually shows I have a full tank or im empty at all times. No in between.

Sounds like the rear fuel pump in the tank is not working and the float or sender is bad also. check to see if the rear pump is working should make a humming noise.

the sender unit in the fuel tank has given up the ghost ,replace unit