Trying to Get Stock Fuel Gauge to Work!!

Hi! I have a 1970 Dart Swinger 318. I had this vehicle about a month now. We are trying to get the fuel gauge to work. So we pulled the dash out to see if we could get the gauge hooked up to work again. But there is no wires whatsoever for the fuel gauge. We looked and looked, nothing!!!! So any suggetions?? I know we can use an Autometer fuel level gauge, but something about the ohm rating of the sending unit needs to be close to the ohm specs of the Autometer gauge?????? Thanks for your help in advance!!!