I am an electrician by trade and have worked in a manufacturing plant for 20 years with automation. Also, I know how hard it can be to find a reason for a failure.
I have read most of the comments on this brake failing and have noticed it happens after the trailer has been connected...
I agree, but when you do the trailer light check, the running lights are turned on at the start and stay on during the whole test. In my case, the truck lights were on but not on the trailer.
I found that when doing a trailer light check on Ford Pass, that the running lights on the trailer were not working. But when I turned the lights on, they did work. I took the truck in to the dealer. They had to order a module. When they replaced it and tested the system, it threw a code. After...