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Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
Part Number: C56377
In Stock
$78.16
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CURT Custom Fit Vehicle Wiring - C56377
Highlights
- Custom Fit for Your Vehicle: Works with your vehicle's wiring
- Plug-and-Play Install: T-connector plugs in behind tail lights with no cutting or splicing.
- Protects Vehicle Wiring: Powered converter draws power directly from battery to prevent overload.
- Reliable Signal Output: 4-pole flat connector powers trailer turn, brake, and running lights.
- Clean Power Setup: Includes 12-gauge wire to safely connect converter to battery.
- Ready for Towing Gear: Works as the base for 4-way wiring setups and trailer light adapters.
Features to know about
Installs Without Cutting or Splicing: Plug-In T-Connector Harness
Getting trailer lights working shouldn’t mean cutting into factory wiring. The Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector plugs directly into the existing tail light connectors for a quick, secure hookup. Everything fits cleanly behind the trim panels, so you won’t have to splice or guess which wire goes where.
Protects Vehicle Wiring: Powered Converter Design
This harness uses a powered converter that draws power straight from the battery through a 12-gauge black wire. That setup keeps the trailer's lighting circuits from overloading the vehicle’s wiring and protects sensitive electronics from shorts or overloads. It’s a safer way to tow, especially when running multiple lights or accessories on the trailer.
Simple Power Connection: Direct Battery Lead
The harness connects only to the positive post of the battery to avoid electrical issues from other power sources. This direct line ensures stable voltage for the trailer lights and prevents problems like intermittent flickering or system faults. Once connected, there’s no risk of parasitic battery drain when not in use.
Covers the Basics for Safe Towing: 4-Flat Connector Output
The 4-pole flat connector provides what most small and mid-size trailers need—running lights, turn signals, and brake light functions. It’s a standard connection ready to plug into most trailer wiring systems so you can head out knowing your lighting signals are clear and working as they should.
Clean, Hidden Install: Behind-the-Panel Setup
The harness tucks neatly behind trim panels near the tail lights for a factory-style look with no exposed wiring. It keeps everything protected from weather and wear while maintaining easy access if you ever need to test or disconnect it later on.
Specs
Electrical Specifications
- Included black wire gauge: 12 gauge
56377 CURT T-Connector Vehicle Wiring Harness with 4 Pole Trailer Connector
Similar to Tekonsha 118746
This Product Fits The Following Vehicles
- 2017 - 2021 Mazda CX-5
- 2017 - 2021 Mazda CX-5
- 2019 - 2019 Mazda CX-5 excluding Diesel
Customer Satisfaction Score:
95% were satisfied with this product
5% of customers were not satisfied
- Product did not meet expectations
- Wrong item was ordered
- Defective
Ratings & Reviews
4.7
149 reviews
by:
Donald
08/06/2026
If you are unlucky enough to have a faulty unit, not only will you have to disassemble your panels not once but 3 times due to company’s policy. I am an unlucky customer that have a faulty unit and phone customer service was very helpful on troubleshooting the problem. I thought everything was in order for return and being shipped a new unit and sending back one the faulty unit. Then I received a email informing me that I would have to return the faulty one 1st for a refund and then ship the new one when they get faulty unit. So I have 2 choices, pull back cargo area apart to remove faulty unit and wait to be sent a new unit or buy a new unit and change unit then send back faulty unit for refund. When I asked about sending a new one so I only had to disassemble cargo area only once , I received an email saying policy don’t allow that and there was nothing more they would do. So may the odds always be in your favor. I will order another one and hope it is not faulty.
by:
Andy C.
06/02/2026
This harness hooked up easily to my existing wiring and has integrated perfectly with U-Haul’s equipment that I have rented. What really made installing this harness a breeze was using the power port already at the back of my 2018 Mazda CX-5 Grand Touring vehicle. I towed a car dolly with my friend’s Kia Rio on it from LA to Phoenix. And I had no problem with the empty trailer lights or the additional, rear towing lights on the Kia. Both sets of LED lights worked fine for the entire trip.
by:
Aaron
09/10/2026
Everything installed fairly simply and the instructions were straight forward. I always have a good experience with etrailer.
by:
Devin
05/30/2026
I love the product, quick story about it, I had to move back across the country and I needed to haul a small U-Haul trailer with my stuff and I was strapped for cash, but also I didn’t want to buy something cheap and then lose all my stuff while driving, so I took a chance on this product and honestly, I never regretted it. However make sure that whoever you have installed it because I did as well. Make sure to check your blinkers and what not because some shops can apparently set it up and then the pace of your blinker or at least one of them will change pace from the other it has nothing to do with the product, but I put this here so if you buy this product, make sure you have someone you can trust to install it if you’re not doing it yourself but also check your blinkers after it’s installed by the installer.
Overall, I love the product and I’m super grateful I was able to find it on here
Overall, I love the product and I’m super grateful I was able to find it on here
by:
Scott
09/01/2026
I received everything I needed for a quick installation.
by:
Bennett
03/24/2026
Works well for a DIY project. Installed this on my Mazda CX5 for towing a small canoe trailer. Just make sure your battery is turned off while you’re working on installing this. Left the battery hooked up and tried to start the car without realizing the battery died from us leaving the car doors open during install. Initially thought there was something wrong with the wiring but simple mistake of draining the battery.
by:
Jed
04/10/2026
I loved your video on how to install the unit. I also loved the string system that you could screw to the end of the bolt to feed the bolt through the rail. That honestly is the reason I purchased your product versus a competitors. Keep up the good work.
by:
Ron
11/22/2025
2020
Mazda
CX-5
Great value, clear instructions on YouTube, two thumbs up
by:
Josh
12/16/2022
Well, I received the product in a timely manner, the install videos were very helpful and spot-on with how I needed to go about it, and the install went smoothly. Not simple by any means, but not too bad. However, after using this with my trailer 3 times, the running lights connection failed. (That's the brown wire, TM or "trailer marker" from what I can tell.) That's a big pain. I called Curt, and their service wasn't great. Seems to be blaming the trailer itself, and didn't really want to help. I got in touch with etrailer, and they were great. Helped me diagnose the problem, narrowed it down to a failure of this product, and got me set up with an advanced replacement under warranty, so I could pull out the bad one and put in the good one at the same time. So that's fine, but I'm only giving 3 stars, because the product failed me, and it cost me $XX to ship back the bad one, and about 2.5 hours of my time to swap it out. I think if the product works for you the first time, it's a 4 or 5 star product, but ymmv.
by:
Calvin
06/05/2025
2021
Mazda
CX-5
The hitch is good quality and came with all the hardware and accessories needed.The same holds true for the wiring kit.
by:
Dan
07/01/2025
I am not a professional but the instructions were more than sufficient to allow me to complete this installation!
by:
Ray
08/25/2025
Fast shipping. Straight forward installation. Everything works perfectly.
by:
Trevor
02/19/2025
Easy to install - but a fair amount of disassembly required for the CX5 to install; but overall straightforward. I wired the power to a 12v plug as opposed to hardwiring to the battery, works great.
by:
Bud
01/25/2021
The wiring harness I bought for my new hitch receiver fit my new 2020 CX-5 perfectly. Installation was easy, after figuring out how to disassemble the rear end of the SUV. The provided connectors mated perfectly with the vehicle connectors. Running a primary wire from the rear of the car to the battery was a bit of a pain; I'd recommend Curt find a way to tap into an appropriate conductor where the harness is being installed on future versions. Otherwise, everything worked perfectly, and when I got the car put back together the entire installation was invisible with the trailer connector pigtail stored in the spare tire compartment until needed. I'm completely satisfied with this harness, and recommend it highly.
by:
Randy
09/03/2022
Product was easy to install. Great quality. Will continue to do business with Etrailer. Super fast shipping. Thanks
Randy
9/3/2023
Perfection, great quality products
by:
Michael
05/15/2025
2020
Mazda
CX-5
Great product. Easy to install. Instructions were clean and understandable. Great price for comple kit.
by:
William
07/10/2020
2020
Mazda
CX-5
I installed this wiring harness myself on my 2020 Mazda CX-5. The instructional video was REALLY helpful. It showed in detail how to remove the interior panels to gain access to both taillights. The plug in T-Connectors were a snap to plug in. I chose to run the wire to the battery beneath the vehicle but inside the under sound proof panels so the wire is almost completely hidden from the elements. Works great and I would highly recommend this wire harness for a 2020 Mazda CX-5 (I think it works for earlier models as well)
by:
Kevin
08/07/2018
2018
Mazda
CX-5
Not a bad install, it was kind of fun. But, in the video I watched they failed to mention the hardest part: running a 12ga, 12V wire from the battery to the rear of the car. It was a little scary drilling a hole in a brand new car's firewall to get the wire through (I did not want to run it under the car, that seemed much sketchier than running it through the interior.) But I hooked it all up, connected my trailer, and, perfect: all lights work great.
by:
Elias
07/29/2022
I have had this for roughly 1 year. I have used the hitch with the wiring harness several times with no issue. It was all straightforward to install using the videos. I appreciate how the harness stays nice and clean tucked inside the car until I need it and then just put it away again.
by:
Keven
07/21/2022
2017
Mazda
CX-5
Works fine, but a bit of a project to complete. Tips: Toss the instructions and just watch the e-Trailer installation video on YouTube. Before installation, make sure all your lights function properly. Saves headaches in case you end up having to diagnose a post-install problem. When disconnecting the Mazda taillight connectors, insert a small flat blade screwdriver downward into the locking clip. Rotate the screwdriver slightly as you pull the connector apart. Rather than tap +12vdc off the cargo jack, I followed the recommended step of running the power wire all the way to the battery. When running the power wire under the chassis, you dont need to fit your whole body under the vehicle to route the wire. The 10mm bolts, push pin and various cavities are accessible with just your upper body, although if you're a larger person, a floor jack may be required. The 4 pin connector pinouts are labeled, so you can test the installation with a voltmeter if you dont have a test plug or trailer. Finally, several connections require a crimper with yellow aperture, so be prepared. Good luck!
by:
Megan
05/11/2025
Easy installation and works great
by:
Maximus
06/20/2022
2021
Mazda
CX-5
Good Product, does what you need. It is time consuming...
Do Not like the fact they want you to hang the plug wires out the tail gate to plug in you trailer. There is a large grommet on the driver side that could be modified to get a good drop to the hitch. I split it and run the wires through then once it was back in place I siliconed it up.
Do Not like the fact they want you to hang the plug wires out the tail gate to plug in you trailer. There is a large grommet on the driver side that could be modified to get a good drop to the hitch. I split it and run the wires through then once it was back in place I siliconed it up.
by:
Jeff
07/23/2020
2020
Mazda
CX-5
Purchased a Class III Hitch Receiver and wire harness for a 2020 Mazda CX5. Arrived within a couple of days, was well packaged and complete. Hitch installed fine and planning to install wire harness this weekend.
by:
Bret
01/16/2023
2021
Mazda
CX-5
The hitch and wiring harness I ordered came quickly and in perfect shape. Your instructional video was very helpful and made mounting a breeze. I have ordered parts here before and have never been disappointed and will continue to use etrailer in the future. Thanks.
by:
CardsFan
05/20/2025
Relatively easy to install if you know what you are doing. Works well in 2019 Mazda CX-5.
Brooke M.
5/20/2025
Glad the install went ok :) Have you caught any games this season? My nephews are at the game they're playing tonight :) Go Cardinals!
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Info for this part was:
Expert Research:
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Expert Research:
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Edited by:
Lindsey S
Video Edited:
Jacob T
Video Edited:
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Video by:
Dustin K
Video by:
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Installed by:
Cole B
Updated by:
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Updated by:
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Updated by:
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Written by:
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Test Fit:
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Test Fit:
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At etrailer we provide the best information available about the products we sell. We take the quality of our information seriously so that you can get the right part the first time. Let us know if anything is missing or if you have any questions.
Josh
12/17/2023
It has been a year, and the new one I put in is still working great.