I have a 2019 f250 cot 6.2 gasser I was having a problem when connected to my travel trailer I kept getting a trailer disconnected and trailer wire fault on my dash. I replaced the 7 pin connector on both my truck and trailer and now when they are connected all the lights on my trailer work but my trailer brakes don’t operate and I get the trailer wiring fault on my dash. I bought a 7 pin outlet tester and when I plug it into my truck I get a right and left turn signal fault check wiring it also alternates between trailer connected and trailer disconnected. Any ideas could this be caused by a bad ground on my truck.

 

With a simple test light , you can verify if the wiring to the plugs is correct and also if the ground, usually a white wire , is good.