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HOW TO: Junction Box for trailer harness (repair or extend the harness)

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EDIT 03/07/21 Here is a rear J Box: ... https://olivertraveltrailers.com/forums/topic/5271-how-to-junction-box-for-the-7-wire-trailer-harness-under-the-front-dinette-seat/

I did this a while back to get a little extra reach, I added an 8 ft harness assembly , cutting off the excess Oliver harness.

I will just post pics and if you have any questions I will answer them. It is really straight forward, I liked how I could sit down in comfort and work on the box with it clamped to a milk crate. When completely wired, I just moved it back under the A frame and stuck it down with 3M VHB tape, and secured the cables. The Oliver and Hopkins wire colors matched perfectly on MY trailer, there is no guarantee so you must check the diagram and/or use a meter.







Be very careful cutting away the outer insulation, the wires are laid in a spiral and it would be easy to cut them. Use GREAT care!




[attachment file=139739]









Here's the placard for inside the J Box cover:

[attachment file=Oliver Junction Box wiring placard.docx]

I like the ability to troubleshoot the wiring without cutting anything, and I can add extra circuits if I need to, like for my future electric-over-hydraulic brake booster.....  Cool.

NOTE: the box is weather resistant, not completely water tight, though the lid does have a nice rubber gasket..... I added a couple of small drain holes in case any moisture gets inside. It is important to NOT blast it directly with a pressure washer.

John Davies

Spokane WA




Edited by John E Davies
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SOLD 07/23 "Mouse":  2017 Legacy Elite II Two Beds, Hull Number 218, See my HOW TO threads: 

Tow Vehicle: 2013 Land Cruiser 200, 32” LT tires, airbags, Safari snorkel, Maggiolina Grand Tour 360 Carbon RTT.

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Nice post. Very timely for a fellow 2013 Land Cruiser owner.


I picked up our new trailer on this past Monday from the factory with our Land Cruiser. By Wednesday my travel partner and I figured out that the trailer plug was being ripped out of the SUV trailer socket in tight left turns. The first time we thought it was an accident, the second time it happened we stopped to think more about it. The third time was on purpose and was witnessed while executing a tight left turn to get out of a parking lot.


The factory supplied cord is too short for a Land Cruiser. Luckily I’d packed the extension I’d made for my former trailer when I had the same problem (even worse) with my old Toyota 4Runner. We got home without damaging anything.


Nice junction box find. I’m going to order one up.


Thanks John.


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2013 Toyota Land Cruiser 200

2018 Twin Bed Elite II #351


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Ken, here’s how I secure the harness on my 200. I am using a +3” Anderson bar to gain clearance for the Stone Stomper support bar, and it needed just a little extra length. It is defiinitely important that everyone makes sure the harness is not stressed when jacknifed to the left or right, depending on the location of your tow vehicle socket.




The 200 receptacle is way over to the right underneath the bumper, a strange place for it....


Ken, can you post some pics of your truck and trailer in a new thread, with some comments? Or you can add them to my “Land Cruiser 200 Towing Thread” if you like. ...http://olivertraveltrailers.com/topic/land-cruiser-200-towing-thread/


John Davies


Spokane WA

SOLD 07/23 "Mouse":  2017 Legacy Elite II Two Beds, Hull Number 218, See my HOW TO threads: 

Tow Vehicle: 2013 Land Cruiser 200, 32” LT tires, airbags, Safari snorkel, Maggiolina Grand Tour 360 Carbon RTT.

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