I have been fighting wiring and grounding issues on trailers and vehicles for years. they do drive me crazy. but your logical steps to diagnose things were great. The thing with the MyTrailer is potentially an example of "too much technology" is not necessarily a good thing. And Ron's comment also sheds some light on maybe how to deal with this. In my current trailer, I have put my own "voltage sensing relay" on my trailer's charging circuit to stop the trailer from draining the truck's battery. So sounds like F150 has this same type of thing already in place.

Here is a little known fact that may help you. F150’s have a relay on the circuit providing power to the charging pin (the one that charges battery and powers tongue jack). The relay is designed to prevent the truck’s battery from being discharged (dead battery) when not driving. The following steps must be engaged for the relay to close and provide power. Trailer plugged into 7 pin receptacle, engine on, key fob inside cab, trailer selected in menu, doors closed, tap brakes (brake lights trigger relay to close if all other steps complete). The relay is on a slight delay. If you unplug and immediately plug back in everything still works. If unplugged for a few seconds, the sequence must be restarted as the truck doesn’t distinguish your intent to plug back in and the relay will create an open circuit. Trailer lights will work immediately when plugged in, as this relay does not affect lights.

What do you have to do for a trailer with a 12volt jack that plugs in the the 7pin on a trailer with hydraulic brakes that uses a 4 pin connector just for lights?

What year is your truck. I have a 2017 with the tow package. Lariat. I have a trailer and just bought an electric jack as well. Brand new. Installed on the trailer. Connected to the 7pin on the truck and it worked for a minute. Then it stopped working and never came on again. I thought it was the brand. So I bought a new brand. Still didn’t work. Help me get this thing going

My issue is after I put the tester on it I found out I didn't get power from the ground. The tester sees the left and right signal is on but no ground

Driving During a heavy rain storm I notice when trying to stop I had no trailer brakes. I unpluged the trailer and sprayed WD 40 in the plug and the plug in. Had not had anymore problems.

I have been telling my dealership that I feel like the brakes are soft on my camper when pulling with my 2021 f-150. I do a brake check when I leave, I push the brake controller at 20 mph and it never locks the brakes on the trailer. I have the gain at 10 and it is at high for aggressive brake but it never seems like is. I am curious if this is the same problem you have been having. I have been on long trips and I feel like I have no brakes. I stop and take the plug out and put it back in and re choose my trailer. I feel like I may be having the same issues you have been having. Do you think it has been corrected by adjusting the pin connection? I think FORD need to address this issue.

With the recall announced by Ford, today, I guess it makes sense to you now.