I bought a new light/ fan combo to replace and old one in a bathroom. This new fixture has those connectors that are plug and play, so to speak. You simply plug the appropriate color wire from the cable into the corresponding hole in the wiring harness for the fixture. 

The catch is that I have a ground, two hots and one neutral (12-3?)and the harness has a spot for each of them plus an extra white (neutral) that of course my cable doesn't have. Seeing as my old fan/light was wired with the same house wire, should I cut the harness to splice together the two neutrals, or somehow branch/split the neutral and plug into the harness? 

If branching/splitting is the recommended course of action, how do I do that?