I had woes with my Liberty harness.
The factory 7 pin harness that runs from the front (Under the dash and battery) was actually missing 2 wires! (Charge line and left turn signal as I recall) back to the connectors behind your luggage compartment where the second 7 pin harness plugs into. To add insult to injury, the expensive harness purchased from Jeep to make the final "Plug and play" connection to the 7 pin socket had a bum relay in it. I don't recall exactly what didn't work, but I am thinking it was the running lights
. We didn't get very far into checking the rest once we determined the plug and play harness was the cause of that one.
First attempt at wiring the socket revealed the bum relay. With the replacement harness, we found the missing wires from the front of the Jeep. At first we (Eric of Liz and Eric, he is an ex Jeep mechanic) thought it was the second factory plug and play harness, but we discovered the missing wires when trouble shooting the car.
I gave up, not wanting to tear the inside of the car open to run lines in the factory harness from the front, so I took it into my trailer guy and he wired up the 2 missing lines the old fashioned way.
Did you buy the plug and play harness that goes from behind the passenger luggage compartment rear panel to the trailer socket? It's a good bet, given my experience and what Jeep told Eric about it being common for those to fail that that is where the problem is.
Ask Jeep to test the harness, even if it was a factory install.