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T-One Wiring Harness Explanation

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T-One Trailer Wiring Harness Explanation


Today we are going to show you a little bit of wiring. Basically kind of like wiring 101 and what to look for when your going to hardwire into the vehicle. What hardwire means is actually getting to the wire and splicing into them to make a connection. T1 connectors are different. They actually have a connection point and harness which you take apart and fit the T in the middle of that. Now on this vehicle we will show you the typical wiring schematics and a couple variants from that. The typical connection point is like where this wiring comes into the back of the tail light and there is always going to be a connection point, almost always. Older vehicles, it would have just ran straight, but with pretty much of your newer vehicles you are always going to have a snap connection like this. Basically a T1 connector simply would just go ahead and fit in between this harness.

Usually there is a little tab right here that you push down, somewhere on the assembly, and you pull it apart. Then your T connector would actually fit in between here and then your wiring would come off from there. That is essentially how a T connector works. Most of the time you will have just one connection that you make. But occasionally on a T connecter you will have to go from two different places. Basically you will have to tap in behind the driver side tail light and then run a wire to the other side on the T connector to the passenger side also. A lot of T connectors are like that. It is just how the wiring is made because the wiring on vehicles predominantly come in two different varieties. In this application here, the wiring harness actually comes down the driver side and comes across here to the tail light on the driver side, tees off, goes into the drivers light, and then goes on over to the passenger side tail light. Now also, that split right here, instead of it being right here to T off, that could be in the other varieties, goes up further back into your vehicle. A lot of mini vans and SUVs are like this. The harness will have just one going down each side of the vehicle. At that rate you are still going to have to go from one side to the other to make your connection points. Like this particular instance we could tap everything from this side of the vehicle to the harness right here. It is kind of more of the exception then the norm. A lot or times it might not be practical to go right here if you know where the harness is. It might just be easier to make your connections behind the tail light, run it underneath the plastic, across and back to the other side and just keep everything in the trunk area. So you do not have to take apart all of this stuff.


Questions and Comments about this Video

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Needed help.I recently bought a trailer with 4 flat, and tried connecting to my Toyota Tacoma 1998 original manufacture 4 flat connector, and only the light working on the trailer come on, no turn signals or brake lights. However, all the brake lights, signal lights etc... of the truck seem to be working fine. I did a troubleshoot the truck connector and it seems to to be working fine have voltage and in good ground. Did I missed anything? Is the T-one suppose to solve this issue?

comment by: Wesley K. - 23/08/2014


If you have checked the truck connector and you are getting the proper signals to the correct pins then the issue is on the trailer. That is a great first step in troubleshooting to isolate the issue on the trailer or on the vehicle. If the issue is on the trailer using a T-one on your truck would not solve the problem. For your case you would need to troubleshoot the trailer connections. I would check the plug first and check for any signs of corrosion, or damage. Make sure that the trailer is properly grounded and that all lights are properly grounded. Many trailer lights ground through the mounting hardware, so check that out too to make sure they are connected to an appropriate bare metal surface. You may also want to trace all the wires and make sure that there is no damage to the existing insulation and no bare copper showing. If you have a tilt trailer, or trailer with a fold away tounge, this connection point can also cause an intermittent ground issue. Check out the helpful article that I have linked for you below that specifies trailer wiring troubleshooting.

Rachael H - 25/08/2014
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Chrystler 2000 300m is this to old for this product I will be adding electric brakes later should i use something else ?

comment by: clint - 30/01/2013


For a 2000 Chrysler 300M, you can use part 118364 to add your basic 4-Pole trailer harness. From there if you will be using electric brakes on your trailer, you can add a 7-Pole which is the most common connector used for trailers with electric brakes. We have an add-on kit for adding a 7-Poleto a vehicle that already has a functioning 4-Pole. That is part ETBC7.

Patrick B - 08/02/2013
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is this t-one connection for a 2012 rav 4 only for 6 cly,can it be used for a 4 cly as well?

comment by: jsoeph c - 12/12/2012


For a 2012 Toyota RAV4, either 4 or 6 cylinder, you would use part 118412.

Patrick B - 14/12/2012
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I purchased a trailer wiring harness for my 2013 Toyota Corolla and note that it specifies a fused connection to the negative battery terminal in addition to chassis ground - this will be a real pain to route from the front to the back of the car. I dont understand this requirement since the negative battery terminal is also ground.Several years ago I installed a similar kit in my 2006 Toyota Matrix and it did not require this connection.Why does the Corolla harness include this connection?thanksKevin

comment by: Kevin A. - 21/10/2012


The harness for a 2013 Toyota Corolla, part 118459, requires a 12V power lead to be run to the positive terminal of the battery with the fuse holder in-line. That is the red wire with the butt connector coming out of the box. The ground wire, white with ring terminal, comes out of the box and will be attached to an existing ground stud in the rear. The reason that power wire needs to be run to the battery is to provide a dedicated power source. Without this the box will not function. The direct power source allows the trailer system to be isolated from the vehicle system by providing its own power. Without it, the box would have to pull all the power through the factory tail light system which either will not support the load of the trailer lights or is small enough that should something short circuit on the trailer it could damage the vehicle tail lights or wiring.

Patrick B - 22/10/2012
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Info for this part was:

Video Edited:
Andrew K
Installed by:
Jeff D
Video Edited:
Joshua S

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