Hi, I have a 04 liberty with a newly installed 118383 trailer harness. Everything works great on the vehicle, lights brakes etc...but when connected to trailer the left signal and brake lights on trailer do not work. This is not a trailer problem! I have connected to three trailers that work as expected with the same problem - left turn and brakes. The harness 4pins show full connectivity. Need help.

 

Bad ground somewhere or short in one of the wires...
I had the same problem.