The OEM harness wire is, being Japanese, not AWG (American Wire Gauge). Their metric wire size is rated in square mm of conductor: as I recall the harness wires are 1.5mm² which is a bit larger than AWG 16 (1.31mm²), and a bit smaller than (basically unobtainable) AWG 15 (1.65mm²). Using AWG 14 (2.08mm²) would have the wires looking rather large, generally people use 16ga because the wires look about the same size as stock. If you don't care about looks - go with AWG 14.
Very important!!! Use high flex wire. You don't need the "wet noodle" stuff available at hobby shops for wiring R/C cars but using 7 strand wire will lead to metal fatigue and wire failure from the vibration. I recommend MTW "robotic" or "machine tool" wire at the last. Auto store hookup wire is still a bit stiff for my liking. I look around surplus shops for large multiconductor cables from scrapped machine tools - the have a lot of individual wires all color coded. You won't find exactly all the wire colors Honda used but you will almost always find the 10 NEMA solid colors and there will be some system of coding the rest, usually colored lines added.
