Re: truck not charging trailer battery
Here's a link to the Standard pinout of the 7 pin connector
7 pin Connector pinout
As far as the ford here's the color code and function of the wiring that they provide at the bumper
You need to verify the following... install 2 relays in the underhood powerbox and... 1 each Maxifuse 30A in Power box location #16 for the battery charge circuit and #28 for the Backup light circuit.
Ford color code
Brown/White = Running Lamps
Black/Light Green = Backup lamps
Dark Blue = Trailer Elect. Brake feed
Dark Green = Right Turn/Stop Lamp
Yellow = Left Turn/Stop Lamp
Orange = Battery Charge
White = Gnd
This list should be good for '99-04 F-Super Duty Series F-250 thru
you will have to verify these connections with the trailer manufacturer, as they may have different pinouts on their plug.