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  1. Custom Fit Vehicle Wiring
  2. CURT
  3. Custom Fit
  4. Trailer Hitch Wiring
  5. 4 Flat
  6. Powered Converter
Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

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

Item # C56303
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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 C56303 or order online at Free expert support on all CURT products. Guaranteed Lowest Price 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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  • Reviews (13)
  • Q & A (0)
  • Videos (1)
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  • Why etrailer?

CURT Custom Fit Vehicle Wiring - C56303

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

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.


  • 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: 5.0 amps per circuit
    • Tail lights: 7.5 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 trunk floor coverings, scuff panel, and trunk liner 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 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.

56303 Curt T-Connector - Surface Mount Technology - 4 Wire

Replaces 56155

Installation Details C56303 Installation instructions

This Product Fits The Following Vehicles

California residents: click here

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

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Curt Custom Fit Vehicle Wiring - Trailer Hitch Wiring - C56303 Review

Speaker 1: Today we're going to take a look at the Curt T-connector vehicle wiring harness with the 4-way flat trailer connector. Now, this is a custom-fit part. It is designed to fit the 2012 and newer Chevrolet Sonic vehicles and on a custom-fit part I always like to recommend for you to go to our website, use our fit guide, put in your year and model vehicle and it will show you if this part will work for your application. Now, this harness provides this 4-way flat trailer connector at the back of your vehicle to power your trailer's signal lights. It is compatible with 5-pole, 6-pole and 7-pole adapters that we do sell separately on our website. This whole harness does connect very quickly and easily.

Basically you just locate your connection points which will be in the rear cargo area, plug in these T-connectors, one on each side, the driver's side and one on the passenger side, ground your white wire and then run your black power wire to your vehicle's battery.Now, this does include this tail light converter, this black box right here. This is to ensure that your vehicle's wiring will match that of your trailer. It is a powered module. That's why you'll connect directly to the battery to avoid overloading the vehicle's electrical system. This converter is constructed using SMT technology which is surface mount technology.

It gives you more consistent, reliable performance, maximize your trailer light yield and intensity while producing minimal heat. It will also ensure superior operation in a lot of rough road conditions.You'll notice on the 4-way it does come with this integrated dust cap for the 4-way. When you're not plugged into your trailer, put that over the terminal. Protects them from any damage or from the elements. This harness is made in the USA.A few specs on it.

The max on the amperage on the stop and turn light circuits is 5 amps per circuit. On the tail light circuit is 7-1/2 amps total. Now, this part comes with everything laid out here on the table. It has a real nice set of detailed instructions on how to install everything with pictures. Basically when you go to install this you'd go to the rear of the vehicle, to the rear cargo area and gain access behind the tail lights.

You want to start on the driver's side. Take the T-connector that has the yellow wire in it. Unplug the harness from your tail lights, plug this in between there. Then you'll have this white wire, this white wire with the eyelet on it. You want to connect that to a good clean ground. If there's one nearby you can use that. If not, they include a grounding screw. You can make your own ground.Then you'll take the other T-connector with the length of green wire. That goes over to the passenger's side. Run that over there, plug that in. Then what you want to do is this converter, you do want to attach this to a flat surface so it doesn't bounce around. They include a piece of double-faced tape to do that with or you could even use one of the cable ties to attach it down. There's even a little tab on it with a hole in it. You could put a screw in there to hold it if you'd like. Run this length of bonded wire with the 4-way on it out to the back towards the trailer. The remaining wire you need to connect is this black wire and that's your power wire. This is the one that will go to your vehicle's battery to the front of the vehicle. They give you this extra length of wire to do that and some connectors. So take one of your butt connectors, put it on your power wire, connect at one end of the length of wire and then run this wire all the way to the front.Once you get to the front, you don't want to connect this directly to the battery. You want to run it through the in-line fuse holder. Take your other butt connector, put it on there. Connect it to one side of the fuse hold just like that. The other side of the fuse holder, you'll take this eyelet connector, attach it and that'll connect to the battery. Once that's all done, open it up, take the included 15-amp fuse, put it right into your fuse holder. Put your cap right on there to protect it and your system would be all ready to go. They include some extra cable ties to take up any slack in the wiring but that should do it for the review on the Curt T-connector vehicle wiring harness with the 4-way flat trailer connector.

Customer Reviews

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector - C56303

Average Customer Rating:  4.5 out of 5 stars   (13 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.

- C56303
2015 Chevrolet Sonic

Good product Hard to install power feed wire through the Left side of car to trunk . GREEN Wire to right turn signal is approximately 10 inches too short.

- C56303

Worked first time, long enough wiring with good AWG. Install went smoothly by following online video. Thankfully made in Mexico, not a piece of junk from China. Chevy Sonics need trailer lighting wiring added.

- C56303
2013 Chevrolet Sonic

Once again ETrailer saves the day. I bought a small trailer and light package but needed a vehicle wiring harness and nobody I contacted had one. Jesse found one for my Checy Sonic right away that easily plugs in behind the tail lights, ( no splicing the existing wires ) and finished the order in five minutes or less. Once again, I'm very pleased with the costumer service. I haven't had the harness installed yet but I have full confidence it's the right one because I haven't had any problems with previous orders from ETrailer. Thanks again

The wiring harness is working good, no problems so far. I did have someone more qualified install it for me but just being able to locate one at etrailer for a subcompact car made the difference
Joe - 07/21/2019

- C56303

Was one of the easiest wiring harness I ever installed and worked right out of the box.

- C56303

This product was mostly plug and play for the connections at the tail lights; however, running the battery line was a real pain. The directions for removal of the panels and such to get at the tail light wiring were not correct and were somewhat jumbled. The wire that needed to go across to the other side should have been at least a foot longer than it is.

- C56303
2012 Chevrolet Sonic

Easy install with the videos on! It took about 30 minutes!

- C56303

30 minute install

- C56303

Great item. Very easy to install and works great !

- C56303
2012 Chevrolet Sonic

Install was easy. it took about a hour to install . I have not used it yet but I can’t wait.

- C56303
2013 Chevrolet Sonic

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

  • How Can Hot lead Wire Be Run When Installing Trailer Wiring Harness On 2016 Chevrolet Sonic
    Although we do not have a video showing the installation of the Curt T-Connector Vehicle Wiring Harness, part # C56303, on a Sonic, I have attached a helpful article that explains the different methods for running a hot lead wire to a vehicle battery. In most cases you can run the wire through a grommet to get the wire beneath the car. I understand running the power wire under the vehicle is not appealing but you can use wire loom like part # 7509-10 so the wire is protected under the...
    view full answer...

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Info for this part was:

Employee Lindsey S
Edited by:
Lindsey S
Employee Jeff D
Installed by:
Jeff D
Employee Wilson B
Updated by:
Wilson B
Employee Kristina F
Updated by:
Kristina F
Employee Isabelle B
Updated by:
Isabelle B
Employee Amanda M
Written by:
Amanda M

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