Trailer Disconnect Error Message Solved, Tow Connector Issue
The short answer is that the 7-pin Ford OEM replacement connector needed fixing. The story:
I purchased a used Ford Super Duty truck and found the previous owner had damage the tow's trailer connector and bracket. I purchased a new bracket and connector from the local dealer. Installed it and hooked up to find a displayed error message, "Trailer Disconnected".
I went through the fixes posted on the Internet, (ground wires, metered out the connectors on the tow and trailer) but the problem persisted. I even found a posted thread comment that the best connector to use had round pins, but as we all know the industry had switched the 7 pin connector to a flat pin type.
The issue which is applicable to all round 7 flat pin tow connectors is that the pin is a folded piece of metal. Done so to make a contact that could wipe against the the trailer's flat contact. Unfortunately the choice of contact pin metal is not good because the tow's pin needs to act like a spring too. I may have bent the pin when I wobbly pushed the tow connector in.
There are plenty of listing issues with folks having intermittent error message occurring while they are towing, this is likely the same problem. For those problems folks post the use of dielectric grease, and cleaning the tow's pins. This will not help at all for bent pins.
The fix is to use a small screw driver (and flashlight to help see down to the bottom of the 7 pin tow connector). The screwdriver is placed inside the pin and twisted to bend the pin back into shape. I did both sides of the pin the bend is small but effective. This will increase the "thickness" of the pin and this will provide more contact force to the tow's connector. Mine was open circuit!
This fix is simple. There are tester that can be used to check the connectors. But the tester is there to determine proper wiring this issue results from poor contact between the tow and trailer connection.