I have a 2012 LT and I’m installing a new head unit. The instructions are in broken english and I need to know if I have to buy an interface.

Hey folks, Aside from the obvious of pulling the OnStar fuse, is there a way to disable the factory Bluetooth and OnStar's use of the steering wheel controls? I've got an aftermarket unit that I'd like to use the functions with, however with OnStar having power, it takes over whenever you...