That is the stepper motor for the interactive exhaust on your XB12. If you have some sort of aftermarket exhuast on your bike, it is necessary to remove at least the cable for the interactive exhuast. The proper way it should be done it to remove everything completely and replace the motor with a emulator. This makes the computer think that the motor is still there, but you can still run your aftermarket exhaust without it. The function of that motor is so that at various RPM's it opens and closes a flap in the stock exhuast pipe depending on the throttle you apply and the RPM you are at. It helps to increase bottom and mid range power.