1993 Dodge Truck in tank fuel pump & gas guage

The gas guage does not work. I cut out an inspection hole out of the truck bed so I coule easily access the fuel pump. There are wires in the plug in, on the top of the pump housing that screws on to the top of the tank. I need to know witch of the wires is the ground. I think if I reground the ground wire, the gas guage might work again, but I have to get the right wire color