DIY Project, 7 Way Trailer Wiring Harness


If you don’t have a new truck, then you will appreciate this DIY. This is a simple project to install a 7-way trailer wiring harness for my 5th wheel into an F250 truck. The purpose of this is to eliminate connecting the power to the 5th wheel lights by the hitch and scratching the paint on the truck. I also had an instance where the connection got disconnected since the wires got caught on the sliding 5th wheel hitch that I have in the bed of the truck.

That’s when I decided to eliminate the extra stretching of the wires and just install a plugin in the bed of the truck.


Finding the Right Harness for my Truck:

This was the tricky part. My truck was manufactured in the last 6 months of production of the 7.3 engine. This was right before the most popular 6.0 (Not sure why it is popular, but all my research indicates it is not worth buying). So when I am looking for parts, I have to go a year prior to 2003. I learned that in this project. I was able to find the connection that I want on For my truck, it was the Hopkins 41157 Endurance 5th Wheel Wiring Kit. Now keep in mind, your truck might be different so your harness might be different; make sure you get the right one. If you don’t get the right one then your lights and connections are going to wired weird. Like in my case, when I bought the wrong wiring harness and connected it to the 5th wheel and the truck, I pressed the brake pedal and the trailer lit up like a Christmas tree. Literally, flashing every light and all in sync. Soooooo make sure you get the right harness.


I had to ensure the colors of the right wires on the harness matches the ones coming from the truck itself.


wiring harness, 5th wheel project, rv life, Hopkins wiring kit.
Make sure all the wiring colors match between your truck and harness

Figuring Out Where to Place the Connection:

I think this is the easiest part of this project. I placed ours at the driver side of the truck bed since the passenger side has a great connection for my 5th wheel emergency brake loop.

Drilling the Hole in the Bed:

I used the Hole Saw to drill the hole in the bed of my truck. But after this project, I wish I have used the 2X Hole Saw since the Hole Saw bit didn’t even last through the whole project. I had to go to a local hardware store to get another hole saw to finish the project.

Connecting the Harness:

One end of the harness goes into the existing wiring from the truck. The other end goes into the outlet by the bumper hitch; it’s an easy plug and plays. You can’t mess it up. They won’t fit any other way. Well, I take that back. You can do anything with force, so if it doesn’t fit, try the other end.


wiring harness, 5th wheel project, rv life, Hopkins wiring kit.

Connecting the Truck Bed outlet:

This one was a bit tricky. I was under the bed of the truck, while Kate was helping me pull the wires through the hole I created in the bed of the truck.


wiring harness, 5th wheel project, rv life, Hopkins wiring kit.
Hole Drilled

Installing the Cover:

This was the easiest part of this whole project. I didn’t have to be under the truck crawling to connect anything nor did I need to hold the drill for too long. All I had to do was tighten the 4 screws and bam! we’re all connected and the outlet is not going anywhere.

wiring harness, 5th wheel project, rv life, Hopkins wiring kit.
Outlet mounted in the bed of the truck

Testing the Outlet:

Before I tightened and zip tied everything neatly under the truck, I had to ensure that the trailer wiring harness was working great and up to standard. So I backed as close as I could to the trailer and plugged the 7-way connection of the trailer into the outlet. Here we are, all lit up and ready to go. I tested all the lights, the signals, and the brake lights. All worked great and the connections are solid.

Tying up all the Loose Ends:

The harness kit came with very long connections and wires, so I had to either cut the slack and re-wire everything or just tuck it all neatly and zip tie it all, that why I chose to zip tie it since I might need to move the plug in the future.


wiring harness, 5th wheel project, rv life, Hopkins wiring kit.

Items you need for this install:

  1. The 7-way harness for your truck
  2. 3-1/2-Inch Standard Bi-Metal Hole Saw
  3. Cordless drill With some drill bits

Project Cost:

Hopkins Wiring Harness: $61.71 (Model might be different for your truck) 

3-1/2-Inch Standard Bi-Metal Hole Saw: $16.07

Compact Drill: $116.99


Other DIY blogs that might be helpful: 

Weighing Your Truck and Trailer

DIY Project, Vent Cover Install

RV Water Pump Install




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