We bought the Mopar harness, had it installed and when we hooked up our 2012 JKU we had no power. I had spoke to the parts manager at our dealership and he warned me about this problem. He spent 2 hours figuring it out, in the rain, the night he was supposed to leave on a trip.
From what I remember him telling me, most RV's are missing the wire that goes to the back for power. I'm not sure the exact explanation, but I know my husband was going crazy trying to figure it out because I sort of forgot to relay the info to him
Apparently it doesn't matter what harness you use if the wire is missing from the RV. Maybe someone with more knowledge can better explain it. Good luck.
Oh, also we have towed our Malibu boat with the RV for years with no issues, so Mike was sure the problem was in the Jeep. It wasn't, oops