Extra wires are added from factory for camera options, switches...etc. What's inside the OM cable doesn't matter. The OUTSIDE diameter must be the same as OEM. If too small, the factory plastic clamps will allow the smaller cable to slip and hang loose. Then, the tellies will catch this and make a huge mess. Be carefull with overmast Hyd hoses as aftermarket guys want to push their "thinner,stretchy" cables that also slip through a 7400's clamps.
Too thin OM cables or hoses will loosen and cost you over $1000 in parts and labor. By the way, first time doing an overmast hose or cable on a 7400 might take you an entire day. Good luck!