So I have seen some other threads but others don't seem to fit in my situation. We have a 2021 Tahoe that did not have the trailer brake controller installed. However, I can clearly see the harness in the proper location, ready to be added. I purchased the OEM brake controller online and have 2 questions. Do I need to buy a new trim piece with an opening for the brake controller? Should it just be plug and play or do I need to have Chevy program it? A lot of others seem to not have the harness in place but I do... So this should be simple..... Right?