REDSLEDZ71

Hello everyone! I am on my 3rd Sierra and on my third Opt7 sequential tailgate bar. My newest sierra is a 2021 1500 AT4. I am reading the putco harness will plug right in with my Opt7 tailgate bar. Is this true even on the AT4 model? My last 2 I was able to hook into the trailer hook up and now it looks like that is no longer possible. I also have the trailer package. Any info would be greatly appreciated. Thank you!