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CURT

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

Part Number: C56404

79 Reviews | 32 Questions

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$100.73

Retail:$154.95

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1999 Toyota Avalon

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curt custom fit vehicle wiring end connector 4 flat

curt custom fit vehicle wiring trailer hitch end connector t-connector harness with 4-pole flat

curt custom fit vehicle wiring 4 flat plug-in c56404

curt custom fit vehicle wiring trailer hitch plug-in

curt custom fit vehicle wiring trailer hitch plug-in t-connector harness with 4-pole flat connector

curt custom fit vehicle wiring trailer hitch end connector

curt custom fit vehicle wiring end connector plug-in c56404

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2015 audi q5 custom fit vehicle wiring curt end connector 4 flat on a

2015 audi q5 custom fit vehicle wiring curt end connector 4 flat c56404

2015 audi q5 custom fit vehicle wiring curt trailer hitch plug-in on a

2015 audi q5 custom fit vehicle wiring curt trailer hitch 4 flat t-connector harness with 4-pole connector

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Videos

Review of Curt Custom Fit Vehicle Wiring - Trailer Hitch Wiring - C56404

How to Install the Curt T-Connector Vehicle Wiring Harness - 2015 Audi Q5

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SCHEDULE AN INSTALLATION

Quickly and easily install a 4-way trailer connector on your vehicle with this custom harness. T-connector plugs directly into existing wiring. Powered converter reduces strain on wiring system and is made using SMT to ensure superior performance. 1-800-940-8924 to order CURT custom fit vehicle wiring part number C56404 or order online at etrailer.com. Free expert support on all CURT products. Great prices and Fastest Shipping for Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector. Custom Fit Vehicle Wiring reviews from real customers.

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CURT Custom Fit Vehicle Wiring - C56404

Highlights

Custom Fit for Your Vehicle: Works with your vehicle's wiring
Tow-Ready Setup: 4-way flat connector powers trailer lights for safe towing.
Plug-and-Play Install: T-connectors plug inline with taillights—no splicing needed.
Reliable Power Feed: Includes 15-amp in-line fuse and direct battery wire for steady output.
Clean Ground Connection: Comes with self-tapping screw for secure bare-metal grounding.
Expandable System: Pairs with kits like #ETBC7L to add a 7-way or brake controller later.

Features to know about

Installs Without Cutting or Splicing: Plug-In Harness

This harness skips the hassle of tapping into factory wiring. The Curt T-Connector plugs directly into existing tail light connectors, giving you a clean, no-splice install that’s ready to go almost immediately. It’s the simplest way to get trailer lighting without altering your vehicle’s electrical system.

Reliable Power with Built-In Converter and Fuse Protection

The powered converter draws power directly from the battery through an included 15-amp in-line fuse. That setup keeps trailer lights powered without overloading the vehicle circuits. It also protects against shorts or erratic lighting, ensuring stable signals every time you tow.

Grounded for Steady Trailer Lighting: Secure Metal Connection

A solid ground is key for proper trailer light function. This harness includes a self-tapping screw so you can make a firm connection to clean bare metal, preventing flickering or partial lighting. Once it’s grounded right, all light functions work smoothly and consistently.

Standard 4-Flat Connection for Basic Trailer Lights

The 4-way flat connector handles all standard functions—running lights, turn signals, and brake lights. It’s the common hookup for most small and midsize trailers, making it easy to connect and go whenever you’re ready to tow.

Expandable Setup for Future Upgrades

If you decide later to tow a trailer with electric brakes or need a 7-way setup, this harness is ready for that too. It pairs easily with kits like the ETBC7L to add brake controller capability without redoing your whole wiring job.

Specs

Image:

56404 Curt T-Connector - Surface Mount Technology - 4 Wire

Installation Details C56404 Installation instructions

This Product Fits The Following Vehicles

2013 - 2017 Audi Q5
2013 - 2017 Audi Q5 without factory trailer connector
2014 - 2017 Audi SQ5 without factory trailer connector

Customer Satisfaction Score:

96% were satisfied with this product

4% of customers were not satisfied

Product did not meet expectations
Wrong item was ordered
Did not arrive in time

4% of customers were not satisfied

Product did not meet expectations
Wrong item was ordered
Did not arrive in time

4.5

79 reviews

5 Stars		(60)
4 Stars		(10)
3 Stars		(3)
2 Stars		(1)
1 Star		(5)

by: Kent 08/28/2025

2016 Audi Q5

Easy install. I did cheat by fishing the wire through the panels.

Kent One Year Later

8/29/2026

Still working great. Very easy installation.

Jerred H.

8/29/2026

@Kent That's great to hear Kent! Thanks for coming back and letting us know.

by: Bob 07/25/2021

I installed the Curt trailer wiring kit right after I installed my hitch, so some of the access points were already open. If you follow directions and install the converter in the battery compartment, the wiring harness to the tail lights will be too short. I installed the converter in the driver side compartment where the air compressor rides and ran the power wire only to the battery compartment. This provided barely enough length to reach the tail light wiring connectors in the lift gate. Other than that, I followed the directions and everything looks good, all the wiring is hidden behind trim panels, and the harness works great.

Click to Enlarge

Bob One Year Later

7/26/2022

Easy as advertised and I still like it.

by: Jaron 07/15/2026

Plug and play wiring, couldn’t possibly be a simpler installation.

by: Nevin 03/22/2025 One Year Later

Everything worked with Audi's electrical system.
Outstanding!

Nevin One Year Later

3/23/2026

So far - So Good. All the components fit and work.

by: Todd B. 07/29/2025

2016 ford Edge

I installed this connector at the same time that I installed the hitch, so the access process was halfway done already. The instructional video was a great guide, though there are a few suggestions I would make. First, Audi has many types of connectors; it would be beneficial in the video to describe how a connector is removed (squeeze the sides, press the tab, etc.). Second, the length of wire needed to run up the driver's side trim panels, around the hatch hinge, down to the lights is not sufficient if you mount the control box to the 10mm spot identified in the video. I originally mounted the control box there and when the hatch closed, the plastic cover on the driver's side hatch hinge pulled the wires tight, causing the wires to slide across the sharp edge of the cover, slicing the cover of all three wires. I ended up using the included adhesive foam mounting block to move the control box up higher in the driver's side access panel, allowing for enough slack to permit the hatch to close without stressing the wires. Hopefully, taping up the sliced wires will be a satisfactory long-term solution as the wiring is functioning as expected now. Third, I was able to attach the ground wire for the control box to a 10mm stud located right next to the place that the video suggested drilling the self-tapping screw, I was hesitant to put a new hole in metal that close to the wheel well. Finally, after the installation was complete, I received a lighting system error code, after a little playing around with connecting, disconnecting, turing the car on and off, and resetting the error codes via OBD2 (using Carista), the error cleared and everything worked. I don't know exactly what resolved the problem, but I spent about 45 minutes troubelshooting before it worked.

by: Geoffrey 03/11/2022 One Year Later

I did end up using it, but the install is ridiculous. I took it to the Dealer and paid ~ $500 to have it installed. The directions show routing the wires up side thru roof and into lift gate lites. And you have to dissasemble the lift gate door panels, Crazy. Even the dealer did something much simpler.

Jenny N.

3/22/2022

The installation for this harness is a detailed installation. I recommend downloading the manual from the product page as it will give step by step instructions so that you determine the difficulty.

by: Benjamin 06/15/2022 One Year Later

Audi Q5

Installation was decently straight-forward (as much as anything can be with an Audi) and sits nicely. I'm very pleased with how low-profile this hitch is. A great choice if you're looking to tow with your Q5. I will recommend accounting for how low the receiver is when you buy your ball hitch.

by: Nick 06/08/2025

2017 Audi Q5

Very easy install after watching the excellent instructional video.

by: Andrew 09/28/2021 One Year Later

Be aware that the trailer lights do not work with the hatch open but otherwise easy to install and functions as intended.

Andrew One Year Later

10/18/2022

Still working as advertised, happy as can be.

by: Veselin 05/14/2021 One Year Later

I purchase the product and I try it and it was great. I didn't use it a lot of times but all the connectors was fitting very good and it is almost like factory one. That was my goal to be as closest as possible to the factory.

by: Tim 07/18/2023

Shout out to etrailer! Wanted to save some money and do the wiring myself so Ed hooked me up with the right stuff and with a quick tutorial from etrailer online showing a clever and effective shortcut, I had it installed in about 30 minutes. Thanks, the hitch I purchased also installed easy with the online help. 100% will use etrailer for all my trailering needs.

by: Matthew 09/16/2025

2015 Audi Q5

Works like a charm...no cutting or splicing. I highly recommend this product.

by: Shaun 03/05/2023

Good product. Super easy to install. Didn’t have to cut or splice a single wire. Manufacturers instructions are vague and didn’t specify where the wires were located for the brake lights so if you don’t know your vehicle check online and you’ll find info how to install pretty much anything.

by: Steve 10/13/2021

2015 Audi Q5

Product is great, instructions are well done. When installing however, the driver's side wiring was not long enough to mount the unit in the battery well as depicted in the instructions, and the passenger-side wiring length only allowed the wiring to be routed under the trim along the top of the hatchback (not along the scuff plate at the back of the car). The CURT instructions should be updated to make this clearer.

by: Ben 09/02/2020

This harness uses factory original plugs that interface with the vehicle's original wiring harness to make installation a breeze, quite straightforward and seamless. No janky scotchlocks, crappy crimps or poor "splice" jobs to be had here. Some disassembly required, but all the best wiring jobs do. 100% would recommend for the professional installer, although this project may be above the heads of the inexperienced DIYer.

by: Brian 04/02/2022

All in all, it was a very simple install for both the hitch and the lights. Would highly recommend. I do think they could have packaged it a little better, it broke through the box in shipping, but it’s a heavy hitch, so it is what it is.

by: Adrian 09/01/2023

The installation instructions are not detailed enough. Other than that, all good. Easy to install

by: John 07/14/2024 One Year Later

Still working flawlessly! Watched the YouTube videos by etrailer and it made the install easy and quick. Love things that work right the first time with zero issues.

by: Kevin 06/29/2025

Perfect fit for my 2013 Audi Q5

by: Clay 04/04/2025

Watched the video before it arrived, went together without any issues, just make sure you reinstall the bottom trim that has the sensor before testing for power at the plug, there won’t be any power if you have put that trim piece installed

by: Dan 01/01/2022 One Year Later

Flawless instructions and has worked great for over a year! Needs a bracket for the plug!

by: Darwin 07/25/2024

I have not installed it yet, but the order was delivered as promised and I like the fact that this item uses factory plugs instead of splicing or tapping into wires.

by: Michael 11/18/2023 One Year Later

2017 Audi Q5

The harness was easy to install. I did need to purchase a 4 prong socket mount so it would not hang loose from the rear of the car.

by: Salvador 06/25/2022

Works as advertised. Pretty simple install. As usual great quality product(s) from etrailer

by: Jerry 02/17/2023

Installation was easy and it works as advertised. The power wires were a little short and needed to be lengthened. That wouldn’t stop me from purchasing again.

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See what our Experts say about this CURT Custom Fit Vehicle Wiring

Do you have a question about this Custom Fit Vehicle Wiring?

Do You Sell a Plug in 4-Way Connector for a 2018 Jeep Renegade?
Welcome back Howard! We do not have the Tekonsha pn 118651 but I do have a comparable alternative. The Curt item # C56274 you were looking at is also a custom fit 4-way connector for a 2018 Jeep Renegade. It's going to plug directly into the tail light wiring harness in the rear cargo area of your Jeep and provide you with a 4-way capable of controlling your trailer or accessories lighting functions. I've linked a couple of installation videos below to help you get the Curt item # C56274...
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Curt 4-Way Not Operating Left Turn Signal On 2014 Audi Q5
You are going to want to start by checking inside the connectors on the Curt T-Connector Vehicle Wiring Harness # C56404 to verify if any of the pins were bent or pushed out on the connectors. You can also use a Test Light # PTW2993 to test both the power going into the power converter from the different functions and verify the power coming out of the converter as well to verify if it is damaged and would be able to be replaced under the manufactures warranty.
view full answer...
What Trailer Hitch Receiver is Best For 2015 Audi Q5
Hi Gingi, I'm confident that if you had a trailer hitch on your 2015 Audi Q5 you would know it. You can definitely add one, and the best option for that is the Draw-Tite Max-Frame Trailer Hitch Receiver # 75940. I like this the most because unlike other hitches, the Draw-Tite # 75940 is a fit for all models of the Q5, even the hybrids. So it is compatible with your car, and the crossbar is also tucked away behind the bumper so your Audi will keep its look. The only other thing you will...
view full answer...
Recommended Wiring Harness for a 2017 Audi Q5
Chip, all of the wiring harnesses we have like the Curt T-Connector # C56404 is going to include that red wire for brakes. The rest of the wiring goes: -Green for right turn, -Yellow for left turn, & -Brown for taillights. If you don't plan on using a brake controller, then you can leave the red wire disconnected.
view full answer...
Parts Needed to Install Redarc Tow Pro Brake Controller in 2023 Audi SQ8
Hey Mark, so the trailer wiring you would have on your 2023 Audi SQ8 would be a 4-way since it's a sedan so to convert that to a 7-way and wire in a brake controller like the Redarc Tow Pro Liberty part # RED52VR you would just need the part # ETBC7 and you'd be set.
view full answer...
Adding 7-Way and Brake Controller to 2017 Audi SQ5
Hey Mark! You already have the right idea here. To add a 7-way you will need to start by adding a 4-way. I recommend using the Curt T-Connector Vehicle Wiring Harness # C56404. This plugs into the connection points in the rear cargo area and then you will run a hot lead up to your battery. Once you have your 4-way you can use the # ETBC7 you looked at to upgrade to a 7-way. None of this will require splicing into the vehicle wiring. For a brake controller I'll give you two options. The...
view full answer...
What is Needed to Use Curt Echo Brake Controller on 2017 Audi Q5 With 4-Way
Hey Larry, Since you already have the Curt 4-Way # C56404 installed on your 2017 Audi Q5, you're halfway there for what you need in order to install and use the Curt Echo Brake Controller # C51180. The other part you'll need for the Echo is the 7-Way RV Upgrade Kit for Trailer Brake Controller Installation # ETBC7L. This will give you the necessary wiring and 7-way connector for your Audi to use the Echo.
view full answer...
Which Trailer Wiring Harness Fits 2014 Audi Q5 TDI
Hey Michel, I am not sure how the guy in the video you found was able to install that trailer wiring kit on an Audi Q5 but it was not designed as a fit for your vehicle so it wouldn't work for you and you'd need to go with the part # C56404 instead. I wonder if he somehow got his part numbers confused or something.
view full answer...
Installing 7-Way Connector and Brake Controller on my 2014 Audi Q5
If you currently have a working 4-Way plug then using the 7-Way RV Upgrade Kit for Trailer Brake Controller Installation Kit part # ETBC7 kit is a great way to get a powered 7 Way connector on the rear of your 2014 Audi Q5. You can use the Curt No-Drill Bracket part # C57202 to attach the 7-Way to. The bracket will mount around the tube of your hitch and really does a great job staying solid. With this kit using the Curt Echo part # C51180 is an easy way to add a brake controller that...
view full answer...
Recommended Hitch and Wiring Harness for a 2016 Audi SQ5
I would be happy to help you. For a Draw-Tite Hitch on your 2016 Audi SQ5 you will want item # 75940. This hitch is custom fit and bolts directly to your Audi's frame with included hardware. To add a brake controller you will need two separate wiring harnesses because you will need to add a 7-way to plug the trailer into. The first harness you will need is the Curt T-Connector item # C56404. This custom-fit T-connector plugs into your vehicle's wiring harness, which is located in your...
view full answer...
Installation Process for Curt 13136 Hitch for 2014 Audi Q5
Because of where all hitches are going to need to attach to on your 2014 Audi Q5, removal of the rear bumper is going to be a required step regardless of what hitch you're installing; unfortunately there's no way around this. While the process may seem daunting at first glance, it's not terribly complicated and when done with care and patience, you can avoid damaging the bumper. If you're going to be towing with this hitch, you'll also need trailer wiring, a ball mount, hitch ball, hitch...
view full answer...
Trailer Wiring that Fits 2014 Audi Q5
Yes we have trailer wiring harnesses that fit your 2014 Audi Q5 like the Curt # C56404 which installs easily by plugging in line with the taillight wiring of the vehicle.
view full answer...
Will Trailer Hitch Weaken Bumper of 2015 Audi Q5
That's a good question but no, the bumper on your 2015 Audi Q5 will not be damaged more easily and will not be more fragile with the installation of the Draw-Tite Max-Frame Trailer Hitch Receiver # 75940. The bumper support is directly replaced by the hitch, and in fact the bumper support is made of aluminum while the hitch is steel. So the hitch won't negatively affect you (or your pup getting in and out) of your Audi. I also wanted to add that if you plan on doing some towing and need...
view full answer...
Troubleshooting Curt Trailer Wiring Harness Installation on 2017 Audi Q5
The Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C56404 is a confirmed fit for your 2017 Audi Q5 and fits behind both the driver and passenger side rear access panels. I've attached the installation instructions which gives you photos to see the locations. The wires will be long enough when installed correctly. I confirmed this with Curt.
view full answer...
Is There a Trailer Hitch Receiver Rated For Weight Distribution For a 2016 Audi Q5?
As the Draw-Tite Max-Frame Trailer Hitch Receiver # 75940 and all of our other receivers for your 2016 Audi Q5 are not rated for use with a weight distribution hitch this leads me to believe your chassis cannot support the use of a weight distribution hitch. While I could not find any specific information to confirm this the only mention I see of it in your owners manual is to referring to the loading of luggage between your vehicle and trailer when towing. The 4-Way Harness # C56404...
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Where Does Trailer Wiring Store on 2015 Audi SQ5
Not all trailer hitches have trailer wiring mounts on them like the Draw Tite part # 75940 that you referenced. I would even say that most actually do not. Especially on designs like the # 75940 where only the hitch opening hangs below the rear bumper. There just isn't a convenient and accessible place on the hitch for it to be. So in these situations if wiring does need to get mounted and doesn't store inside the vehicle hatch you would attach a bracket to the rear bumper fascia. The...
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Recommended Trailer Hitch and Wiring for 2014 Audi Q5 Hybrid
I recommend using the Curt # C13136 on your 2014 Audi Q5 Hybrid, which will provide you with a 2" hitch receiver that is well suited for towing a trailer. It looks like your Q5 hybrid has a 4400-lbs towing capacity, so you'll want to make sure that you stay under that to avoid damaging your vehicle, but this hitch will allow you to tow up to that capacity. Since you're going to be towing, you'll also need trailer wiring, a ball mount and hitch ball to complete your towing setup. For wiring...
view full answer...
Trailer Hitch for a 2015 Audi Q5 to Tow a Boat Trailer
The most popular trailer hitch for your 2015 Audi Q5 is Curt hitch # C13136. This is a Class III trailer hitch with a 2 inch receiver, and then for trailer wiring to add a 4-way use part # C56404.
view full answer...
Troubleshooting Curt Wiring Ground Connection on a 2015 Audi Q5
Hey RJ, thanks for reaching out about installing the Curt Wiring # C56404 on your 2015 Audi Q5! You are right on the money about the ground. It needs to be securely connected to a clean, bare-metal surface on your vehicle. This kit comes with a self-tapping screw so what we typically do is find a metal spot to install that screw to. Hope this helps!
view full answer...
Can Prodigy P2 Brake Controller Install in 2015 Audi Q5
Yes you can install a Prodigy P2 part # 90885 in your 2015 Audi Q5 that currently does not have any trailer wiring. For that you would need to start with a 4-way like the part # C56404 which installs easily and does not require hardwiring to the vehicle. Next you'd just need the part # ETBC7 which comes with everything needed to convert the 4-way to a 7-way and wire in a brake controller.
view full answer...
Wiring Harness Fit For 2014 Audi Q5 Premium
While we do have a trailer wiring harness for your 2014 Audi Q5 Premium, I checked with Curt and the part you mentioned is not a fit. Instead, the correct wiring harness for your Audi is the following: - Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C56404 I verified with Curt that the # C56404 is compatible and will fit your '14 Audi Q5 Premium so you can power your trailer lights. It will work perfectly in conjunction with the hitch that fits your car,...
view full answer...
Will the Curt T-Connector Vehicle Wiring Harness C56404 Fit a 2013 Audi Q5 Hybrid
The Curt T-Connector Vehicle Wiring Harness part # C56404 is a confirmed fit for a 2013 Audi Q5 Hybrid. It offers plug-n-play installation as well so there will be no splicing into any wires on the vehicle. It provides a standard 4-way flat trailer connector that has all the basic trailer lighting functions. If you don't already have a trailer hitch, the Draw-Tite Trailer Hitch Receiver part # 75940 is what I recommend because of the hidden cross tube. It offers bolt-on installation as well.
view full answer...
Best Trailer Wiring Options for 2017 Audi Q5
For your 2017 Audi Q5, yes, the part # 119250KIT would work. It is a no-spice install and comes with the power wire you'd run up to the battery. I attached an install video link for this for you to check out on a very similar 2018 Q5 as well. Not to make your choice any harder but we also have the Curt harness # C56404 which is custom fit instead of universal so it would also be a very easy install.
view full answer...
How To Secure Curt Echo On 2015 Audi Q5
The best option to secure a trailer connector on a 2015 Audi Q5 with a trailer hitch like the Draw-Tite Max-Frame Trailer Hitch Receiver part # 75940 is the Curt Easy Mount Bracket part # C58000. This will provide a safe and secure connection for the 7-Way RV Upgrade Kit part # ETBC7L and Curt Echo Wireless Trailer Brake Controller part # C51180. The Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # C56404 is an excellent option as well.
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