No, you don't want to cut any wires except to get the correct lengths. Any unused circuits/wires will be looped and tied up under the dash. You probably want to mount that fuse box upper left of your left foot in the cab. But low enough to get at fuses. Engine, front light and rear light harness branches will go thru the firewall in 1,2 or 3 places depending. the dash and cab branches stay inside cab. Install dual sockets front and rear first. Take out old harness sort of in one piece, here and there.
