Okay, I think I understand. The wiring at the receptacle reverse was just providing a pathway for shorts to occur. I missed the part in the initial post where turning on the four ways or anything to do with the brake lights would activate the brakes. That, along with the "check trailer" warning could certainly account for the messages.
Two different messages; "trailer fault" is saying "hey, there is power on the brake feed that shouldn't be there" or short some place, "check trailer" is saying "hey, we lost connection with the trailer". Oops on my part!