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!
The aftermarket fuel gage is likely spliced in to the factory fuel tank sender wire somewhere under the dash, and the wire going up to the cluster is either cut, or was tapped into.