Jeep Wrangler JK: How to Install Trailer Harness

Installing a wiring harness is a lot simpler than people may tell you, so read on to learn how you can install one in your Jeep Wrangler.

By Bassem Girgis - November 17, 2015

This article applies to the Jeep Wrangler JK (2007-Present).

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.

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.

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.

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.

Figure 4. Disconnect tail light.
Figure 5. Connect trailer harness to tail light harness.
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.

Figure 7. Feed trailer harness through.
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.