You did it, but no, your friend did it, you are not a car junky but you supervised your friend install the stuff....sounds like your a union worker. On-Star employees deployed at dealerships...... this is getting entertaining.
May I suggest another potential blame recepients? What about your friend and instructions from AAC?
Bottom line, you knew what you did and no one forced you to take the rental. You knew there was an underlying fact. If I know there is a chance after a more thorough inspection and not a desktop problem troubleshooting analysis, that the blame will rightfully circle back to me because of the goof-up I did, I would not accept any free offers from the dealer, not even a free coffee!
Pay for it, it is your fault, live and learn. Short cuts and backyard mods can sometimes lead to bigger problems and cost more to correct than if you paid a pro to do the work in the first place.