We bought an L with trailer prep, and than purchased the hitch and harness we had the dealer install it all when we hooked it up to our horse trailer it told us to check connection and light out. We also got the yellow trailer warning symbol. The running lights will not work. But that horse trailer works with our other truck, and our L works fine with 4 other horse trailers at our barn. Our trailer has old lights and the rest have LED. So, we had Jeep look at it again and they said they fixed it, but they didn't. We also tried to hook it up tonight to a small older hybrid travel trailer and received the same problems. Any suggestions?