Truck Repair: fuel, dodge cummins, fuel gauge

Question
I have a 1993 dodge cummins 1 ton  the fuel gauge dosent work I checked the wires for power and there is a blue,green,and black wire the blue had very little power the green had noting and i think the black would be a ground where do the wires go and what would be the problem

Answer
Most all fuel gauges work off a rheostat(fuel sending unit) to change the voltage to the gauge for needle to move.The best way to check fuel senging unit is to remove it  from the tank & ohmn it out while moving the float manually checking the resistance.If it changes,then float is working.