Fuel Gauge and Sending Unit

Hey I was wondering if anyone has info on the tank sending units that would be found in a 67 Cuda. My gauge provides no reading. I have tested my gauge and it works..and I have tested the wires and they flow proper curent..so Im assuming the problem is in the sending unit. Out of all the experiance my family has with wrenching on cars its for some reason still a mystery..how many wires should be coming off the sending unit? One or two? I have little experiance in this area as of yet. Anyhelp would be appreciated! Thanks!