Fuel gauge wiring question

When I purchased my 70 Swinger, it had an aftermarket fuel gauge under the dash, due to what I soon discovered was a missing needle on the factory fuel gauge. I managed to find another correct fuel gauge to put back in, but I dont know how to rewire it. I havent taken the cluster out yet, so I thought I would ask in advance if anyone knows what I do with the wire coming from the tank. Wiring is not my specialty...haha
Thanks for any help!