new guage

I am replacing the old fuel gauge with a new Equus fuel gauge in my 76 Dart Sport. I found the blue wire coming from the sending unit, it goes to a connector by the kick panel, on the driver's side and from there to the old fuel gauge. There is a cluster at the gauge with at least 10 wires. My question is:after the connector the blue wire changes gauge(becomes smaller), is this the correct wire, is it safe to assume it is? Should I just cut it there and splice to the new gauge? (I am replacing the old gauge with a new one because the old one stopped working)