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  1. Custom Fit Vehicle Wiring
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FITS 2017 Mazda CX-5
Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

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

Our Price: $56.73
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Custom Fit Vehicle Wiring
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2017 Mazda CX-5

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Call at 1-800-940-8924 for expert service. We are your Mazda custom fit vehicle wiring experts, and offer a great price. carries a complete line of CURT products for your Mazda CX-5 2017. Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part C56377 from CURT can be ordered online at Complete custom fit vehicle wiring installation instructions and technical support.
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2017 Mazda CX-5 - Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

  • Custom Fit
  • Trailer Hitch Wiring
  • 4 Flat
  • Powered Converter
  • CURT

Quickly and easily install a 4-way trailer connector on your Mazda CX-5 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.


  • Provides a 4-way flat trailer connector at the back of your vehicle to power your trailer's signal lights
    • Compatible with 5-pole, 6-pole and 7-pole adapters (sold separately)
  • Connects quickly and easily
    • Locate connection points in rear cargo area
    • Plug in T-connector
    • Run hot lead to car battery
  • Includes a tail light converter to ensure that your vehicle's wiring matches that of your trailer
    • Powered module connects directly to battery to avoid overloading vehicle's electrical system
  • Constructed using surface-mount technology (SMT) for consistent, reliable performance
    • Maximizes trailer light yield and intensity while producing minimal heat
    • Ensures superior operation in rough road conditions
  • Comes with dust cap for 4-way flat connector


  • Maximum amperage:
    • Stop/turn lights: 3 amps per circuit
    • Tail lights: 6 amps per circuit
  • Limited 1-year warranty


This custom-fit T-connector plugs into your vehicle's wiring harness, which is located in your rear cargo area. You will have to remove the floor coverings, storage trays, rear scuff panel, and side trim panel to access this harness. Once you've plugged in the T-connector, run the hot lead up to your car battery. Connect the lead to the included fuse holder, and then connect the fuse holder to the positive terminal on your battery.

Once installation is complete, the 4-way connector will be stowed in an out-of-the-way location within your rear cargo area.

It is recommended that you use a small amount of grease on all electrical connections - the plugs on your automobile and the 4-pole connector itself - to help prevent corrosion.

Powered Tail Light Converter with Surface-Mount Technology

A tail light converter is built into this T-connector. This converter is a circuit-protected, battery-powered unit that bypasses the electrical routes that are used by a basic wiring harness. As a result, there is virtually no draw on your tail light circuits.

Because most trailers run on a two-wire system - wherein the brake and turn signals are carried on one wire - the separate brake and turn signals from your vehicle's three-wire system need to be combined so they are compatible with the wiring system of the trailer. This converter combines the brake and turn signal functions of your automobile so that they run on one wire to properly activate your trailer's tail lights. Note: This will not affect how the tail lights on your vehicle operate.

Curt builds each tail light converter using surface-mount technology (SMT). This method of construction involves soldering electronic components directly to the surface of a printed circuit board. SMT eliminates the need for leads, which are used in older through-hole technology. The result is a circuit board that is smaller yet provides more routing area and that offers superior performance, reliability and durability.

Curt SMT Circuit Boards

Circuit boards constructed using SMT have been shown to perform better under rough conditions with excessive vibration than those made using the through-hole method. And where would vibration be more likely to occur than in towing applications? Curt converters also produce less heat, leading to increased durability and longer life. In addition, lower levels of resistance ensure better performance, especially for parts that operate at higher frequencies.

Each Curt circuit board is made using high-quality components that are pieced together in the most technologically savvy fashion, leading to greater predictability and reliability in functioning.

56377 CURT T-Connector Mazda CX-5 Wiring Harness with 4 Pole Trailer Connector

Item # C56377

Installation Details C56377 Installation instructions

California residents: click here

Customer Satisfaction Score:

Customer Reviews

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector - C56377

Average Customer Rating:  4.8 out of 5 stars   (86 Customer Reviews)

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.


I think the quality of the wiring harness is horrible. I got the plug and play harness and now my left turn signal flashes like my bulb is burned out. Their not so I took it to the dealership and they said the box where all the wiring goes to is faulty. They disconnected it and it is fine. The problem is I don’t have the box or receipts to send it back. It would be nice if you rectify this problem and I would gladly change my review. This is the 4th hitch and wiring harness that I bought from you.

The harness does have a 1 year warranty. I will have our Customer Service team reach out to you.
-- Etrailer Expert Jenny N - 10/12/2022


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.

2019 MazdaCX-5

Great product, coupled with the very helpful videos from etrailer. The installation was very straightforward, and it seems to be working great in my 2019 Mazda CX-5. No complaints at all here, and for getting a 4 pin connector on my vehicle, I think I made the best choice.


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.


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!


Sturdy trailer hitch for my 2018 Mazda CX5. The installation video couldn't have been any better.


This is my second trailer hitch from etrailer. Everything has been as described; very good quality and on time


wire harness did not work right for my auto.

The # C56377 you purchased is a fit for the 2017-2021 Mazda CX-5 only. For the 2022 model, youd want to use # TK85VR
Mike L - 10/16/2022

2021 MazdaCX-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.


Well thought out set up. A dream installation with the plug and play wiring harnesses. Took my time (especially when popping the back panels on my wife’s brand new vehicle) and still only took a couple hours start to finish. Definitely recommend this product.


Product was easy to install. Great quality. Will continue to do business with Etrailer. Super fast shipping. Thanks


Great product. Instructions included were worthless, but the video was excellent. Did not have to cut any wires, since I had a rubber plug I could cut to accommodate the 4-pole connector.


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.


Overall I think this is well made and a very reasonable price. I think the install time is longer than what you suggest. Also, I believe it requires 2 people to install. My only complaint was the 2 sided tape was dried out and would not stick to the car or the module.


Easy to install and works great. Hardest part was running the wire to the battery.


This install went well and was truly plug-and-play. I elected to tap power off the 12v jack in the rear luggage compartment rather than run a dedicated line all the way up to the battery. (I never use that jack anyway.)


Does what it needs to. Pretty hard to i nstall.


This was very easy to install with minimal problems. Also purchased wire harness and install also was mighty easy. Since install, I pulled three trailer loaded with around 2K lbs of pavers to my house with no problem. Very Happy.


Works perfect for my 2018 Mazda CX-5 easy to install for the first time ever!

2022 MazdaCX-5

Good product easy install. Only hard part was running the wire under the car to the battery. If the car was on a lift would’ve been much easier!


I am returning this because it is supposed to be plug and done. Well, I had to route a wire from the battery to the back of the vehicle. I found another one that doesn't require that step and draws power from the back junction box. Easier.


Good product and delivery ??


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.


excellent service and prices,I ordered a hitch, but the wrong wiring kit. after looking again i saw a alert that the wiring kit ordered was not certified for my this was the next day and my order had already shipped I called and after a brief wait, spoke to adam
he checked my order and confirmed, i had ordered wrong wiring kit.HE WENT OUT OF HIS WAY TO SHIP THE CORRECT KIT THE SAME AFTERNOON. he also e mailed a return label for my incorrect order. cant say enough about the good service and quality staff they have employed there...

2020 MazdaCX-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)

Show More Reviews

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

  • Does Wiring Harness on 2019 Mazda CX-5 Have to Get Power From 12V Battery
    The Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C56377 will always be connected to a battery so it will be "on" in the same way that everything else that is connected to the battery of your 2019 Mazda CX-5 is "on." That said, there are no negative effects, problems, or issues whatsoever with it being connected to your Mazda's battery. The only problems that will arise are from attempting to power the connector from anything but a direct hot lead to the...
    view full answer...
  • Does Curt Trailer Wiring Harness # C56377 Have Label On It
    The Curt harness part # C56377 does not have a label on it. Thank you for the picture but what you have is correct! I checked your order notes and you received the correct harness too.
    view full answer...
    Image 1 for
  • Options for Running Power Wire of Curt Trailer Wiring Harness # C56377
    The connection to the battery is something that many people have reservations about until they actually start the process and realize that it is not so bad. There are different ways you can get to the battery and we actually wrote an FAQ article on this topic which I have linked for you. The FAQ gives general tips on different methods for routing the power wire. You can run the wire through the vehicle if you wish but just keep in mind that this does take more time and you may end up...
    view full answer...
  • Why Does Trailer Wiring Harness for 2017 Mazda CX-5 Require Running Wire to Battery
    Not all vehicles can handle the additional amperage draw of the trailer taillights on the vehicle taillight circuits. Those vehicles need setup that draws power from the battery. Some vehicles have higher rated circuits that can handle this, and others need to have the power drawn straight from the battery to protect the taillight circuits. For your 2017 Mazda CX-5 you need to install a harness that draws power from the battery to protect the taillight circuits. For that you would need...
    view full answer...
  • Troubleshooting 3rd Brake Light Not Working on 2019 Mazda CX-5 After Installing Curt T-Connector
    You might want to go back through and trace the steps that you took when installing the Curt T-Connector # C56377 on your 2019 Mazda CX-5 to see if you accidentally forgot to plug something in or if maybe some wiring got damaged. Since the tail lights are working properly I don't see how the T-Connector would be affecting the 3rd brake light but if everything looks fine you might as well disconnect the tees from the Curt wiring harness and plug everything in like it was prior to installation...
    view full answer...
  • Easy to Install Trailer Wiring Harness for 2020 Mazda CX-5
    I checked with Curt and they just recently confirmed the fit of their trailer wiring harness # C56377 for your 2020 Mazda CX-5. This is a custom install kit so the install would be super easy as well!
    view full answer...
  • The Lights On My 2018 Mazda CX-5 GT Alternate With The Trailer Tail Lights When Pressing The Brake
    What you are experiencing is normal for your Curt T-Connector # C56377 on your 2018 Mazda CX-5 GT. The powered converter is taking the input from your vehicle lighting and distributing it out to the trailer tail lights. It may seem odd but there is no reason to be concerned as the lights are all working properly.
    view full answer...
  • Wiring Harness Installation Instructions for a 2022 Mazda CX-5
    The Curt Wiring Harness with 4-Pole Flat Trailer Connector item # C56377 for the 2022 Mazda CX-5 attaches behind the rear tail lights. You will have to take apart your cargo area to remove the trim pieces to access the tail lights. The T-one harness plugs in line with the tail light harness so you won't have to cut or splice any wires. I have linked a video that shows the entire installation process including the removal of all cargo area trim to access the tail lights.
    view full answer...
  • Is There Parasitic Battery Drain For Curt Wiring Harness C56377
    No, there is not a risk of parasitic battery drain for the Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C56377.
    view full answer...
  • Does Curt Trailer Wiring for 2020 Mazda CX-5 have to Wire to Vehicle Battery
    We can't recommend you use any power source for installing the Curt # C56377 other than the positive post of the battery. This allows you to completely bypass the wiring of the vehicle so that in the event of a trailer wiring short it doesn't hurt the vehicle wiring.
    view full answer...
  • What Gauge Wire Is Included With Curt T-Connector Vehicle Wiring Harness # C56377 For The Battery?
    The included black wire which connects the Curt T-Connector Vehicle Wiring Harness # C56377 to the battery is 12 gauge.
    view full answer...
  • Troubleshooting Turn Signals Not Working When Running Lights On Following Installation of Curt 56377
    The turn signals should definitely work while your running lights are on. Based on what you are describing you need to check the ground wire connection on your # C56377. Make sure it is secure on a clean, bare-metal surface. The other possibility is the connections from the T-connector aren't secure. You can unplug them and plug them back in to make sure they are seated properly.
    view full answer...
  • Difference Between Wiring Harnesses for 2019 Mazda CX-5
    Between the two wiring harnesses that fit your 2019 Mazda CX-5, Tekonsha # 118746 and Curt # C56377, I recommend the Tekonsha. It has a higher maximum amperage than the Curt. Another reason I recommend the Tekonsha is simply because we've always had better success with their reliability. I also prefer how the Tekonsha's converter box actually uses a screw to anchor it in place where the Curt's is just doublesided tape.
    view full answer...
  • Can Wiring Harness be Installed After Hitch on 2017 Mazda CX-5?
    To answer your first question, yes, you would be able to install wiring after you have put in Draw-Tite # 76138. In regards to your second question, the answer is it depends on the harness. For example, Curt T-Connector # C56377 is a confirmed fit for your 2017 Mazda CX-5, and it could be installed without drilling.
    view full answer...
  • Trailer Wiring Comparison for 2017 Mazda CX-5 Tekonsha Compared to Curt
    For your 2017 Mazda CX-5 we have two trailer wiring harnesses available. The Curt part # C56377 and the Tekonsha part # 118746 which you mentioned. In general the Tekonsha kits are more reliable and less likely to short out. Partially due to the fact the Tekonsha has a higher amperage rating: # 118746 Stop/turn lights: 5 amps per circuit Tail lights: 7.5 amps per circuit Compared to # C56377 Stop/turn lights: 3 amps per circuit Tail lights: 6 amps per circuit
    view full answer...
  • Can the Rear Accessory Socket on a 2017 Mazda CX-5 be Used to Power the T-One # 118746
    Although the recent CX-5s may have a power source bus in the hatch area you will want to run the wire for power to the battery. The Tekonsha T-One # 118746 is a new kit for 2017+ Mazda CX-5s which Tekonsha designed specifically for your vehicle. Since both Tekonsha and Curt (for the Kit # C56377) say that you need to route the power wire directly to the battery that is the best route to go. After routing the wire up to the battery you need to install the included fuse and connect it to...
    view full answer...
  • How to Install a Trailer Wiring Harness on a 2017 Mazda CX-5
    We have not yet had the chance to install a trailer wiring harness on a 2017 Mazda CX-5 so I would not have any additional advice for you outside of what is laid out in the instruction manual. However, I see you purchased the T-One Vehicle Wiring Harness part # 118746 which means you would have received the instructions included with this kit which I agree are rather vague. However, the process to install the trailer wiring harness will be the same as the Curt T-Connector Vehicle Wiring...
    view full answer...
  • Recommended Trailer Wiring Harness for 2019 Mazda CX-5
    Curt and Tekonsha both offer wiring harnesses for your CX-5. The Tekonsha model is # 118746 and the Curt is # C56377. Both install in the same manner, by plugging inline between the vehicle's taillight assemblies and the wiring harness that feeds them. No cutting or splicing required. Because the Tekonsha # 118746 has a higher amperage rating 5 amps/each stop/turn circuit and 7 amps/each taillight circuit as opposed to 3 amp/6 amps for the Curt model, I'd recommend the Tekonsha. Aside...
    view full answer...
  • Trailer Wiring Comparison for 2019 Mazda CX-5 Curt or Tekonsha
    For your 2019 Mazda CX-5 we have two trailer wiring harnesses...the Tekonsha kit part # 118746 that I recommend and the Curt # C56377 which is also a solid choice, but the Tekonsha is the better route. The reason I recommend the Tekonsha is because it will be more resistant to internal shorts of the converter box due to shorts on the trailer's wiring. This is mainly due to the higher amperage rating of the converter box (7.5/5 amps compared to 6/3 amps of the Curt) and because in general...
    view full answer...
  • If asked to choose between the Tekonsha # 118746 or a Curt # C56377 I'd go with the Tekonsha. The Tekonsha model has a higher amperage rating, and over the years we've found their electrical products to be slightly more reliable in the long run than those from Curt. Curt makes a great product, but the Tekonsha is just a little bit better. If you click the provided link, you can see the harness I recommended being installed on a 2017 CX-5. The procedure on your vehicle would be identical.
    view full answer...
  • Comparing Tekonsha and Curt Trailer Wiring Harnesses for 2019 Mazda CX-5
    Both the Tekonsha T-One Vehicle Wiring Harness # 118746 and the Curt T-Connector # C56377 are designed to fit your 2019 Mazda CX-5, and will install in the same manner by plugging into existing ports behind the trim panels in the vehicle's rear cargo area. Both also require a hot lead to be run up to the battery for power. Between the two options though I do recommend the Tekonsha T-One # 118746 because it features a higher amp capacity for its circuits and also uses a superior converter...
    view full answer...
  • Trailer Wiring Harness Recommendation 2020 Mazda CX-5
    Tekonsha and Curt both offer trailer wiring harnesses for your vehicle. Between the Curt # C56377 and the Tekonsha # 118746, I'd suggest the Tekonsha, as it has a higher amperage rating at a pretty similar price. If you click the provided link, you can see a video of the harness being installed.
    view full answer...
  • 4-Pole Flat Wiring Harness for 2020 Mazda CX-5
    I would be happy to help you select a wiring harness for your 2020 Mazda CX-5. The Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector item # C56377 you were looking at does fit your vehicle but I recommend going with the Tekonsha. The Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector item # 118746 connects in line behind your CX-5's rear tail lights and plugs directly into the lighting harness. This will provide you a 4-pole flat connector...
    view full answer...
  • What is the Difference Between the Tekonsha # 118746 and Curt # C56377 Wiring Harnesses?
    As far as comparing the Tekonsha T-One Wiring Harness # 118746 to the Curt T-Connector Wiring Harness # C56377, there are more similarities than differences. As far as similarities, both harnesses will provide you with 4-way access on your vehicle to power your trailer's signal lights. Also, both are compatible with 5, 6, and 7-pole wiring adapters and include a hot lead wire that attached to your battery. For the differences between the two harnesses, the Tekonsha harness runs at a higher...
    view full answer...

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Info for this part was:

Employee Mike L
Expert Research:
Mike L
Employee Jameson C
Expert Research:
Jameson C
Employee Lindsey S
Edited by:
Lindsey S
Employee Jacob T
Video Edited:
Jacob T
Employee Chris R
Video Edited:
Chris R
Employee Dustin K
Video by:
Dustin K
Employee Jonathan Y
Video by:
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Employee Cole B
Installed by:
Cole B
Employee Wilson B
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Employee Amanda M
Written by:
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Test Fit:
Shane H
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