Chris,
Great work...appreciate you posting your install thoughts. I’m getting ready to use the LLJ harness (once it’s shipped) for my 2019 Sierra Denali. I saw a video they posted where they tapped into the signal under the passenger side dash. For your truck ( and I’m assuming mine) did you use the harness at the Bose amp that you said was behind the rear seat? I plan on using a JL fix 86 and not the lc7 that LLJ would have sold with the harness. I need to find that YouTube video you mentioned about removing the rear seat if that’s where I need to connect the harness .
Ron