If I purchase an onstar and steering wheel interface for an 04 Impala, do I need any additional wiring to keep from having to cut and solder to factory plugs

an onstar as in the factory system as far as i know you cant just add one that system is tied into all the vehicles wiring so i dont know about getting one of those and as for using the sterring wheel controls you need a device called the pac swi* the * represents the particular model for your car i would check their website