I've added/repaired many electric fans on cars it would be the same on motorcycles, first I would highly recommend controling it with a 30 amp relay. a relay is a way of controling high voltage with low voltage with a 30 amp breaker built in. This is how it should be wired 87 & 86 go to hot,the factory hot wire controlling the fan you would cut. run the bike untill fan kicks on, cut the wire, the hot side of the wire would go to 87a, the other side of the wire going to the fan would go to 30, use a 2 pole switch or push button one side to 85 the other to ground if you have to control it manually dont worry about cutting or splicing the factory harness you stand a good chance of burning up the harness or bike if you dont use a relay