"OEM Harness" would be the factory connections at the triple. While you don't HAVE to take things apart to make that connection, it sure makes things easier (unless you have tiny hands). The right upper fairing and trim panel will expose where the stock horn connects (and give you room to get your hands in there). It's just a couple spade-type electrical connectors, so pretty simple disconnect. You might even be able to do it from below by removing the small trim panel above the radiator, but still not a lot of maneuvering room from down there.
