This applies to 2007 trucks, as far as I know. However, it is similar to installing it on 2004-2008 trucks, but the fuse box might look a little different.

This is a quite simple process... in fact, only 7 steps.

You may click on any picture for a higher resolution.

1. Remove the old 4 pin wiring harness, if the truck came with one. To remove, simply disconnect the two connectors, and using an 8mm socket, unbolt the ground screw which is located on top of a cross member on the frame. Remove spare tire of needed -- although not necessary. After completing that, it should look the the picture below with the harness removed. Note the red stars.



2. Get your new harness which is Ford Part Number: 5L3Z-13A576-BA and compare the old (if applicable) to the new. You will notice that it has a 7 pin wiring connector AND a 4 pin wiring connector for added convienence. It should look like the picture below, with the old being on the left (4 pin) and the new being on the right (4 pin + 7 pin).



3. Repeat Step 1.

4. Then get your 7 pin plug and plug it in to the new harness. The Ford Part Number for the 7 Pin Trailer Plug is: XL3Z-14489-BA. Securely snap it in place. Then get a zip tie or two and zip tie it to the bumper, or be creative and make mount. If you have installed the Ford Trailer Hitch, you can then get the optional plate, which is Ford Part Number: 5L3Z-17C886-BA. However, for my install, I just simply used two zip ties.

5. Open passenger side door, and look below the glove compartment, and you will notice a small door on the right. Open it. Then you will notice a black box, feel around on the bottom and there is a clip, pull down and pull out. This will then reveal your fuse/relay box. I would suggest printing out the below diagram for reference, and check each fuse and relay as you go. Make sure they are of proper amperage as well. Fortunantly mine only needed Relay #05. Some trucks already have the fuses and everything, but it is simply just missing a relay. Mine was only missing one, so I was lucky. Some that don't have the factory trailer towing package might not any of the trailer tow fuses and relays at all. So be wise, and when you go to order your parts for this project, print the diagram below out and carefully go thru and check. Remember, like with wood working, measure twice, cut once. Same with working on projects. You don't want to be hung up waiting for parts, because of lack of poor planning on your part. After installing all the fuses and relays, repeat the first steps and snap all covers securely in place.



Relay #05:


Print this out:


6. Get your brake controller and a wiring harness. I bought mine from etrailer with the pre-built F150 wiring harness. In this example, we are using the Tekonsha P3 digital brake controller, which at the current time, is one of the highest regarded brake controllers on the market. Once you have the wire harness built, open the driver's side door and look underneather the dash, in-line with the brake pedal. The connector is quite close to the OBD port. Connect your wire harness to that connector and then SECURELY mount your brake controller to your preferred location. However, ALWAYS follow the manufacturers instructions for proper mounting, wiring, and safety guidlines. Remember: This device needs to be mounted as the manufacturer intended, failure to do so, can result in damage to the vehicle, trailer, and even death or serious injury to users and bystanders. Don't be alarmed if the brake controller powers on when you plug it in. That is a constant 12V circuit.
For plug location, look at star in picture.

Connector, with harness plugged in.


Tekonsha P3 Mounted and Ready For Use:


7. Whew! Almost done. Get a multimeter or a trailer wiring tester and test your wiring. I've got a light tester on mine in the below picture, but I used my Fluke Multimeter with a helper to test the electric brakes to ensure I was getting voltage. If everything checks out ok, then you are good to go! Go get your trailer and plug it in and try it out. You will need to adjust your settings on the brake controller to your braking tastes.



With that said, enjoy!

 

ManualF150 - I just wanted to say thank you for this. I used your how-to to successfully wire up my 2008 F150 XL (also a manual) to the 7 pin wiring and added the Tekonsha P3 to boot.

I know the post is old - but it was very helpful no less.

 

I also want to thank you. The harness was a perfect match up to my 2007 F150 truck and also the R05 relay that was needed. Everything went just as smooth as could be. The only difference I used the Prodigy RF brake control system. It's a great system if you have multi vehicles you tow with or loan it out to your buddies.

 

Any after market harness direct fit to the oem connection available ? Ford oem parts are pricey.
Have 2008 FX4

 

Try etrailer.com.

 

Been looking all over , including etrailer but no dice . The ones on etrailer show a different connector than mine . They are either round or square , and mine is rectangular. I really don't want to cut and splice , or use the 4 pin to 7 pin adapter , requiring the hot wire and the trailer brake wire to be spliced in as well.
The factory harness is the only thing I've found so far that is plug and play.

 

Etrailer even has a video showing a 7 pin t- connection harness install on a 2004 , but says it won't fit 2008 on the website.

 

I did the same thing for my 02 back in the day...the parts were inexpensive from ford and only took a few minutes to do...

 

The harness alone from ford is over a hundred bucks. 7 pin outlet was 35 plus the bracket . Maybe a trip to the salvage yards is in order or just space in the hopkins 4 flat to 7 pin conversion kit . It's only 35 bucks for everything you need , just takes a little more effort is all.

 

Here are some tips (many years later) if you are using an aftermarket kit like Hopkins 47185:

* FYI You can easily and temporarily Swap relay 6 (blower motor) for 5 if you are missing or waiting on that part.

* On the factory rectangular connector, there are two heavy gauge wires going into the “corners” of the connector. One is orange — that is the relay 5 switched power to the trailer. The other is blue — that is the ‘blue-brakes’ line to the brake controller. In my aftermarket Hopkins kit, I spliced in the Black (supply) and Blue (brake controller).

* Connect the existing 4 pin to the 4 pin on the aftermarket adapter. Mine was corroded to heck so I just cut the ends off and spliced the 3 wires (left white cut off since there’s a better ground elsewhere)

* There is a reverse signal somewhere in the factory rectangular connector but I couldn’t decipher it, so I tapped into the line directly on the left brake light (two 5/16” bolts to remove the light). This went to purple on the aftermarket.

* I paired up the aftermarket ground with the factory ground and used the existing bolt on the top of the crossmember. I was lazy and didn’t want to dig out self tapping impact driver blah blah

This was the laziest way I found to get the job done on my (now old) truck. This is also the best way to use an aftermarket adapter since the factory wire nest has everything nicely fused and relay controlled.

Appreciate the original post and everyone’s comments above — thank you!