How to Install a Trailer Harness on a Jeep Wrangler JK

Chris

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For the Jeep Wranglers that don't come with a wiring harness, it becomes a problem when you want to tow a trailer. If you tow a trailer without connecting the wiring harness, you won't have tail lights or brake lights activated on the trailer, which would result in a hefty ticket. Installing a trailer wiring harness could be a complicated job if you want it to be; however, if you buy a tail light wiring harness, which is an adapter that connects to your tail light and takes the power from it, the job can take no time and can be done successfully. Read on to learn how you can easily install a wiring harness on your Jeep Wrangler and start towing your trailer.

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Materials Needed
  • Phillips head screwdriver
  • Wrench
  • Trailer wiring harness
Step 1 – Disconnect battery
Whenever you're working with anything electrical in your Jeep, it's recommended you disconnect the negative (black) battery terminal. Use your wrench to loosen the negative battery cable and wrap it in a towel so it doesn't make contact with anything metal.

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Figure 2. Disconnect negative battery terminal.

Step 2 – Remove tail light assembly
The tail light assembly is held in place with four Phillips head screws. Remove all four and pull the assembly out.

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Figure 3. Remove tail light assembly.

Step 3 – Plug wiring harness
With the tail light assembly removed, unplug the tail light bulb from its electrical harness. Then install the trailer wiring harness to the tail light electrical harness, and install it to the tail light bulb. The trailer wiring harness should have three ends. One attaches to the tail light harness, the second one attaches to the tail light bulb, and the third one is an oddly-shaped wiring harness, which is the one that attaches to the trailer's wiring harness.

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Figure 4. Disconnect tail light.


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Figure 5. Connect trailer harness to tail light harness.


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Figure 6. Connect other end to bulb.

Step 4 – Feed trailer harness through
Feed the trailer harness end through the tail light hole, and through the bottom foam liner. Make sure to pull it enough that it will be able to reach the hitch to connect to the trailer.


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Figure 7. Feed trailer harness through.


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Figure 8. Feed it through foam liner.

Step 5 – Install tail light
Feed all the wires through the tail light, then install the tail light. Tighten all four screws that holds the tail light assembly in place, but don't tighten too much or it will brake the plastic cover. Attach the wiring harness' push connector to the frame rail. The frame will have holes equipped specifically for that. This prevents the wiring harness to dangle around and get caught with something. Mount the trailer plug to the hitch.

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Figure 9. Install tail light assembly.


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Figure 10. Connect wiring harness to frame rail.

Featured Video: Jeep Wrangler Trailer Wiring Install

 
Quote from above:
Step 2 – Remove tail light assembly
The tail light assembly is held in place with four Phillips head screws. Remove all four and pull the assembly out.
End quote.

The photo of the red jeep shows the wrongs side, the yellow jeep photos are correct.
Also just the 2 inside screws need to be removed.
While in there check for mud salt and rust. I sprayed a little fluid film on the gas filler line as there was a little surface rust.

FYI
$45 hitch fit fine and has excellent welds and came with wiring harness.
I had to wedge the muffler forward a little to insert the bolts. short 2x4 spacer and a plastic wedge did the trick.
https://www.amazon.com/gp/product/B00P32VQEE/?tag=jkforum-20
 
If you're wanting to wire your plug into your harness I can help with that. Something to keep in mind is trailer wire colors and vehicle wire colors are NOT the same. Even different makes and model vehicles use different color wires, which is quite aggravating.
Trailers colors are as follows:
White=ground
Brown=power (running lights)
Yellow=left turn
Green=right turn
Blue=back up lights
Now are short white and blue wires, those go to the brake actuator to keep the brakes from locking up while backing up.
If you have an electric brake or hydro/electric brake system things more complicated and colors start crossing.
That being said, I wired my plug into my tail lights. On the left tail light I did the yellow (LT) onto the white with green stripe. Brown (pwr) goes to white with orange stripe. White goes to black (seems backwards but haven't had any issues). On the right tail light I believe it was the white with purple stripe is green (RT). And the back ups.. honestly I forgot. I can take a look if you need me to. Hope this helps.

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If you're wanting to wire your plug into your harness I can help with that. Something to keep in mind is trailer wire colors and vehicle wire colors are NOT the same. Even different makes and model vehicles use different color wires, which is quite aggravating.
Trailers colors are as follows:
White=ground
Brown=power (running lights)
Yellow=left turn
Green=right turn
Blue=back up lights
Now are short white and blue wires, those go to the brake actuator to keep the brakes from locking up while backing up.
If you have an electric brake or hydro/electric brake system things more complicated and colors start crossing.
That being said, I wired my plug into my tail lights. On the left tail light I did the yellow (LT) onto the white with green stripe. Brown (pwr) goes to white with orange stripe. White goes to black (seems backwards but haven't had any issues). On the right tail light I believe it was the white with purple stripe is green (RT). And the back ups.. honestly I forgot. I can take a look if you need me to. Hope this helps.

The color code depends on which standard was followed. The vehicle will likely follow the SAE standard color code, but RV's follow the NFPA-1192 standard for a 7-Pin connector. In my experience (somewhat limited but have some), utility trailers follow the SAE but it depends on the sourced parts.

trailerwiringcode.png


Simple, right? :) At least the functions are the same at each pin position for both standards.
 
The color code depends on which standard was followed. The vehicle will likely follow the SAE standard color code, but RV's follow the NFPA-1192 standard for a 7-Pin connector. In my experience (somewhat limited but have some), utility trailers follow the SAE but it depends on the sourced parts.

View attachment 123666

Simple, right? :) At least the functions are the same at each pin position for both standards.
Ok, that's a helpful diagram. Not trying to argue about anything, just trying to provide some knowledge. I've been building trailers for a living for 8 years. I've never seen a wire harness with purple on it. It's usually a light blue running the length of the harness for back ups and a short darker blue for the brake actuator. The black and red/orange is for electric brakes. As far as vehicles it's never as simple as "the yellow wire". I've wired vehicles and it's usually white with yellow stripe, white with yellow and orange stripe, white with yellow and black stripe, white with... so you either have to get a vehicle specific diagram or use a wire tester and start trouble shooting to narrow it down. Anyways if someone has questions I'll be willing to try to help. -new guy Erik.
 
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