I don't know if this has been addressed before. I did search some of these threads and was unsuccessful in finding anything relating to my issue. I'm trying to take the factory trailer wiring for a 7-pin wiring which terminates on a cross member just before the spare tire. I have purchased a wiring diagram and went to the Ford Dealership. I have not found a wiring diagram that has the same color wires as pictured below that are actually on my 2011 F150 XLT. I'm just trying to reach out to see if anyone has a wiring diagram or knows how I might be able to come across one. I want to know what each wire does before cutting the factory harness to splice wiring harness to run to the bumper for the 7-pin trailer adapter

 

There is a much simpler way to determine what color wire is what.
You might also find wiring diagrams don't always agree with your particular vehicle.

Here is how you determine which wire does what,
Clip a test light to a good ground, turn on the parking lights and the wire that causes the test light to lite is for parking/tail lights.
Do the same thing with left turn signal, only one wire will cause the test light to blink, and then right signal and so on.
If the stop lights are separate from the signal lights only one wire will have power when the key is on and the brake pedal is depressed.

Black or Brown wire is for running lights.
Yellow and Green are for signal lamps, Red is usually for stop lamps and Blue is usually for Aux lighting,charging a remote battery etc. or whatever you choose to use it for.
WHITE is used for GROUND ONLY..
Because problems can come up, It is a good idea to note where each fuse is for each function.

 

We have access to the Ford schematics, but you should be able to purchase the harness extension and 7/4 way connector..

 

Thanks for the input. I have so put a fuse and a relay in for the Trailer brake controller and still was not able to get any signals at the plug I need to splice into. I have now bought a used Ford Trailer brake controller and activated the computer controller for it. On the next warm day, I do plan to trace the harness wires to find the functions.

 

Tried to back probe wires. With the box off the harness you can not front probe as truck will not start with out it. With truck in accessary mode only get power but no other signals. Apparently Ford does not know what wiring that they put in what trucks because dealership was unable to give a wiring diagram with same colors that are in my truck. Do they use any available wiring at the time, Im at a loss.

 

If you want to , you might consider this,

Make a sketch of the plug in question with the 7 contacts in it.
Start your vehicle and idling with the vehicle in Park or Neutral if std trans, and parking brake applied.
You can do the same checks with a simple test light
Tail-Running lights
Left signal
Right signal
Stop lights , if separate
Ground
Aux.
Using a test light ensures you make no mistakes because going by wire colors can sometimes get you into trouble.