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Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End

Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End

Item # C57187
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Convert your vehicle's 4-way flat trailer connector to a 5-way flat. Plug the 4-pole connector into your vehicle and connect the wire leads to get the electric brake function. Lowest Prices for the best trailer wiring from CURT. Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End part number C57187 can be ordered online at or call 1-636-306-4830 for expert service.
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  • Reviews (67)
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CURT Trailer Wiring - C57187

  • Wiring Adapters
  • Single-Function Adapter
  • 5 Flat
  • Plug and Lead
  • 4 Flat
  • CURT

Convert your vehicle's 4-way flat trailer connector to a 5-way flat. Plug the 4-pole connector into your vehicle and connect the wire leads to get the electric brake function.


  • Adapter converts your 4-way flat trailer connector to a 5-way flat trailer connector
  • Additional wire leads for reverse lights
  • Durable molded plastic construction resists corrosion
  • Simple installation
    • Wiring harness plugs into existing 4-way flat connector and hardwires to existing wiring


  • Wire configuration:
    • Green: right turn signal and brakes
    • Yellow: left turn signal and brakes
    • Brown: tail lights
    • Blue wire: reverse lights
    • White wire: ground wire
  • 1-Year limited warranty

57187 Curt Trailer Connector Adapter - 4 Way Flat to 5 Way Flat

California residents: click here

Video of Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End

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

Video Transcript for Curt Wiring - Wiring Adapters - C57187 Review

Speaker 1: Today we're taking a look at a Curt trailer connector adapter four-way flat to five-way flat for the vehicle end. This adapter converts your four-way flat trailer connector on your vehicle to a five-way flat trailer connector to work with your trailer wiring. It does come with additional wire leads for electric brakes. The connectors are molded. It's a durable molded plastic construction, which is designed to last a long time and resist corrosion. Pretty simple installation.

The harness plugs into your existing four-way flat connector at the back of your vehicle and it hard wires to the existing wiring for the electric brake function. And then this right here is your five-way flat, which would connect to the five-way flat on your trailer.This wire right here has the pre-attached connectors on it, so this is the one that would hard wire to the vehicle. You've got the bare end on this side, then you have the connector right here, which mates up perfectly with the connection point on the wire that comes from the five-way flat. It's always a good idea to go ahead and wrap that up, maybe in some electrical tape or put a heat shrink outer wrap on that to seal it up, keep the elements out. This piece right here measures 36 inches.

This piece right here measures 26 inches. And the wiring between our two connectors measures two and 1/4 inches.That's gonna do it for today's look at the Curt trailer connector adapter four-way flat to five-way flat.

Customer Reviews

Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End - C57187

Average Customer Rating:  4.8 out of 5 stars   (67 Customer Reviews)

Convert your vehicle's 4-way flat trailer connector to a 5-way flat. Plug the 4-pole connector into your vehicle and connect the wire leads to get the electric brake function.


My newly acquired boat trailer(previously owned) wiring hookup didn’t match my SUV wiring connection so I purchased this adapter. Working very well thank you.


Great design and quality. Now I just need to figure out where to tap into the backup wiring on a 2021 Sienna so that I can use this to trigger the brake lockout solenoid on my trailer when backing up.

Still works great after a year. And I did figure out how to connect to the backup wiring in the tailgate so my trailer brake lockout works too.
Barry B - 04/27/2022


Once I figured the right wire for the reverse lights, I had it all hooked up in 10 minutes. Easy Peasy, thanks for all the customer help when I called in.


I bought this product a year ago. My car was wired for a 4-prong utility trailer and last fall I purchased a small 5-prong motorcycle trailer that I intended to pull with my very small car. I needed this adapter to make everything work correctly on both units. It's perfect. The folks at e-Trailer are always super helpful and they pointed me to this one right away, knowing exactly what I needed (I had no clue - I'm a novice!) Once again, both the staff and the product came through for me 100%.


Quick install, highly recommend the ada pter.


Item delivered ahead of schedule and exactly as advertised. Adapter is a real problem solver. Assistance by sales staff was fast and professional.


I cannot give this item a fair rating as the trailer lights on my 2016 trailer do not work. The trailer is in absolute MINT condition so no problem there. I had the wiring checked on my 2011 Toyota Siena, everything there checked out A-OKAY, but when I attached the adapter to my Van/Trailer wiring, nothing, no lights. I talked with a gentleman from etrailer but he was of no help and not able to offer a possible solution. The wiring harness was installed on my Toyota three years ago for a different trailer that took a 4-way flat to a 4-way flat and worked flawlessly with that trailer.

Anytime theres a trailer wiring issue, the first step is to narrow down where the problem actually is. Use a circuit tester like # 40376 or a multimeter to test each pin on the trailer connector as a helper applies the brakes, uses the turn signals and turns on the headlights. This will confirm the functionality of the wiring harness on the vehicle. Next, plug in the # C51787 adapter. Test each pin on the adapter as its function is activated. If all checks out okay, youve ruled out the vehicle and the adapter as being the problem, which leaves the trailer. Weve seen wiring problems on brand-new trailers, so its entirely possible that the problem could exist on the trailer, regardless of its overall condition and appearance. To test the trailer lights independently of the tow vehicle, you an use a 12 volt battery. Ground the battery to the trailer frame, then apply power from the positive battery post to each pin on the connector and see if the lights for each circuit illuminate. Ill also link you to some Help articles about trailer wiring. One article will help you understand the basics of how a trailer wiring system works, the other helps with basic troubleshooting.
-- Etrailer Expert Mike L - 05/15/2018


Works as intended. Easy to wire up. Just splice the blue wire into your vehicles reverse light wire and your good to go. Works great for my boat trailer with led brake & reverse lights


I would had given a 5 star if the tracking was more accurate


Just what I needed to wire my new boat trailer to my truck.

Works perfectly. I like its tight fit for a great conection
Hugh H - 08/08/2021


Works like a dream


Excellent product. Exactly what I needed to hook up my five pole trailer to my four pole truck.

Still working as well as it did on day one. 5 star product.
Leonard E - 05/09/2021


Product came on time as expected. The adapter is working as described. Thank you!


EXCELLENT PRODUCT.. Re-wired my trailer with LED and reverse lights; not realizing, these lights come with an extra plug. The converter adapter was exactly what I needed. Tried to just splice the wires together...naw, bad idea! Use the adapter; it works.


solved a wiring problem that has bothered me Perfect length of adapter Order was delivered faster that promised.


Seems to be exactly what I needed for converting my four pole vehicle side to a 5 pole trailer side. The installation video was very helpful.


Works great with older vehicles


Installed on a 2017 Jeep Wrangler unlimited. Product arrived as stated. Easy to install took abou 10 minutes. I have pulled my boat several times lights work and the main reason was to dis-engage the surge brake when in reverse. Works great!!


I purchased one of these and it was exactly what I needed except I messed up the install so had to order a second one. Before I'd ordered the first one, I'd contacted them looking for a solution for my specific situation and their answer was very thorough and clear. Great customer service. Highly recommend working with this company. Their products are high quality and fairly priced.


Second item that I ordered from etrailer.I was able to easily track it and it arrived quickly. Perfect fit from my new truck to my boat trailer. Thanks for the excellent service!


etrailer folks are terrific. When ever I call they have a solution for the situation at hand. In this case I needed an electrical connector to adapt my boat trailer to a new vehicle and Robert knew exactly the correct product to use. Courteous friendly help as usual.


Great products. Grt service also I have bought from etrailer b4 and always been happy


Just what I needed to get my surge brakes from engaging on uphill backups! The video for my 2019 Highlander helped immensly. Toughest part was wiring tot he reverse light circuit but once that's done no more surge brake "backup" headaches.


Worked great, no problems with install or use.


Solid product. Worked as advertised and very easy installation. And Will Call worked great...ordered and picked up in the same day:)

Show More Reviews

See what our Experts say about this CURT Trailer Wiring

  • Correct Trailer Connector for Boat Trailer with Surge Brakes and Electric Lockout
    In most cases, boat trailers with surge brakes and an electric lockout solenoid use a 5-way flat trailer connector. In which case, you will need to install the Curt Trailer Connector Adapter part # C57187 and that's it. This will plug into the 4-way and then splice into the reverse light circuit.
    view full answer...
  • How To Activate Surge Brake Reverse Solenoid On Vehicle with 4-Way Harness
    In order to activate the reverse solenoid on the brake actuator you will need to converter the 4-way trailer wiring harness you have to a 5-way using the Curt Trailer Connector Adapter part # C57187. This adapter will then plug into the 4-way on the vehicle and allow you to hook-up the 5-way on your trailer but you will need to run one wire from the adapter to the reverse light circuit on your vehicle. In order to find the correct reverse light circuit on your vehicle you will need to obtain...
    view full answer...
  • 4-Way to 5-Way Adapter for 2019 Toyota Highlander Towing Boat Trailer
    To convert the 4-way of your 2019 Toyota Highlander to a 5-way requires the 4-way to 5-way adapter part # C57187. This plugs into the 4-way you have now and then gives you an additional wire you'd run to the reverse light circuit of your vehicle. To prevent wires from being visible would require you to route the wire behind interior panels on it's way to the reverse light wiring.
    view full answer...
  • Recommend Adapter To Change 4-Way Trailer Connector To 5-Way On 2019 Ford Ranger
    The most common connectors on boat trailers are the 4-way and 5-way flat connectors. The 5-way flat connector is easy to identify as it looks just like the 4-way connector but will have one extra pin. If your trailer has a 5-Way flat connector you will need the Curt Trailer Connector Adapter # C57187 which will plug into the existing 4-way connector on your 2019 Ford Ranger and will require you to run the blue wire up to your reverse light wire for use with surge brakes. If you do not...
    view full answer...
  • Recommended 4 way to 5 way adapter for 2014 Ford Explorer
    In order to use your 2014 Ford Explorer's 4 way with a trailer that has a 5 way connector you'll want to use the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187. You'll just want to tap into the reverse light circuit on your vehicle, as you mentioned, to make the additional connection live for the trailer wiring. You can find the reverse light circuit by tapping into the wire of the reverse light on your tail lights.
    view full answer...
  • Can You Use A 4-Way Flat Trailer Connector With A 5-Way Flat Vehicle Connector
    You will not need an adapter to plug a 4-way Flat Trailer connector into the 5-way Flat Connector on your vehicle. You will just have one pin un-used on the vehicle side connector which is for the reverse lights. This is commonly needed for trailers with surge brakes. The only time you would need an adapter like the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat # C57187 is if the connectors were reversed and the trailer had the 5-way flat connector in which case an adapter...
    view full answer...
  • How To Hook Up a Trailer With 5-Way To a Vehicle With 4-Way
    In order to hook up a trailer with 5-way flat to a vehicle with 4-way flat you need to use the Curt Trailer Connector Adapter part # C57187. That blue wire will need to be spliced into the vehicle's reverse light circuit but there is no way around this as the trailer will require it. In order to find the circuit you'll have to do some testing with a circuit tester.
    view full answer...
  • 4-Way To 5-Way Flat Connector Adapter
    You just need this adapter # C57187. The blue wire will tie into a wire on your 2017 Tacoma and then snap into the blue wire with the connection point. I have a video to help explain more!
    view full answer...
  • Is the Orange or Brown Wire the Hot Wire in My Back Up Light? And How to Find Out.
    The brown wire is usually your running lights but for all wires on your trailer you can apply a source of power from a 12V car battery to see what function each wire activates. You should connect the battery's negative terminal to the trailer frame and then apply 12V power to each wire to see what each wire connects to. This should help you to identify which wire does what on that tail light. I attached a FAQ on trailer wiring for you to check out also. You can refer to it for trailer...
    view full answer...
  • How Do I Run My Backup Lights from the Trailer into My Cab of My 2000 Peterbuilt?
    In order to run the backup light into the cab, all you need is the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187. This harness will allow you to convert your 4-way harness to a 5-way with the additional backup light pin. If you currently have a 7-way installed, I recommend routing some spare wire from the reverse signal on your 2000 Peterbilt to the 7 way and then into the trailer's reverse lights.
    view full answer...
  • Parts Needed to Add 5-Way Trailer Wiring Harness to Vehicle with 4-Way
    You'd just need a 4-way to 5-way adapter part # C57187 which will plug into your active 4-way and give you a wire you'd need to run to the reverse light circuit of your vehicle which would then be active whenever the vehicle is put in reverse.
    view full answer...
  • Availability of 4-Way to 5-Way Adapter for 2008 Lincoln Navigator Towing a Boat Trailer
    In order to add a 5-way connection to your 2008 Lincoln Navigator you need the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187. You will plug the adapter into your existing 4-way connection and the additional wire will connect to your reverse lights to send the signal for your electric lockout. I have attached an installation video for your reference.
    view full answer...
  • Where Does Blue Wire of 4-Way to 5-Way Adapter Need to Run
    Yes, if you connect the blue wire of the Curt trailer wiring 4-way to 5-way part # C57187 to the reverse lights of your tow vehicle it will activate the reverse lockout solenoid of your trailer wiring and will allow it to be reversed without applying the brakes.
    view full answer...
  • 4-Way to 5-Way Adapter for 2003 Chevy Express Van Towing Trailer with Surge Brakes
    What you need is a 4-way to 5-way adapter like with the Curt # C57187. This plugs into your 4-way and has a wire you'd run to your reverse light circuit and use the included quick splice to attach to. This will give you a functional 5-way like what your surge brake coupler needs.
    view full answer...
  • How To Install 5-Way Trailer Connector On 2015 Jeep Wrangler Unlimited
    I do have an option for you but there are only 4 and 7-way trailer wiring harness options for a 2015 Jeep Wrangler Unlimited, I recommend the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118416 for a 4-way. This can then be adapted to a 5-way using the Curt Trailer Connector Adapter part # C57187. The blue wire must be spliced into the reverse light circuit on the vehicle. This can indeed be best found behind the tail light. You will need to test each of the wires...
    view full answer...
  • Can You Use 4-way To 5-way Adapter Without Connecting Blue Wire To Vehicle?
    You can use an adapter like the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187 and just cut the blue wire off the adapter since you are not needing to use the reverse lights. This will not be in reverse, as the adapter is designed to convert a 4-way vehicle connector to a 5-way trailer connector exactly like you are wanting to do This will protect the 5th pin of the 5-way connector from debris and corrosion over time and will not cause any shorts or wiring...
    view full answer...
  • Tapping Into 2021 Toyota Sienna Backup Circuit
    I recommend installing the Curt Trailer Connector Adapter # C57187 on your 2021 Toyota Sienna similar to how we installed this in our video linked below. I was informed by Toyota that you will be tapping into the red wire in the harness as that is the reverse light circuit wire. I recommend confirming that you have the correct wire by using a Test Light # 40376.
    view full answer...
  • Recommended 4-way To 5-way Adapter For Motorcycle Towing Motorcycle Trailer
    Typically the blue wire on a 5-way connector is for reverse lights. If you do not need the reverse lights you can actually just plug the 4-way connector directly into the 5-way connector. If you need the reverse lights to work you will need a 4-way to 5-way adapter # C57187 installed on your motorcycles 4-way and will need to connect the blue wire to the reverse light wire with the included quick splice. I included a video of the # C57187 being installed for you to take a look at.
    view full answer...
  • Adapter To Convert 4 Flat To 5 Flat On A 2011 Nissan Pathfinder
    The Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187 is what you are looking for in this situation. Included are a couple of video resources providing an overview as well as an installation walk through to help you get started. Basically you will plug into the existing 4-Way on your Pathfinder. The blue wire then gets spliced into the reverse circuit wire on the vehicle for the reverse lockout on the boat trailer.
    view full answer...
  • Recommended Wiring Harness for 5th Wheel With Separate Circuits to Have a 4 Way Connector for Towing
    I recommend usiing the Tekonsha Upgraded Tail Light Converter with 4 Pole Flat # 119130 that you were looking since it will combine the brake lights and stop lights from your 5th wheel trailer into a combined system and provide you with a 4 way connector at the same time. This eliminates the need for using normally separate parts and really streamlines the installation process for you. If your 5th wheel has a reverse light circuit and the trailer you'll be tandem towing has a 5 way with...
    view full answer...
  • How To Add a 5-Way Flat Trailer Connector To a 2017 Toyota Highlander with Tow Package
    In order to add a 5-way flat trailer connector to a 2017 Toyota Highlander you'll need to start with the Curt T-Connector Vehicle Wiring Harness part # 56042 which is plug and play and has a 4-way flat connector. Then, you can add the Curt Trailer Connector Adapter part # C57187 to convert the 4-way to a 5-way. The blue wire gets spliced into the vehicle's reverse light circuit. Unfortunately, they don't offer a one piece 5-way flat trailer connector for most vehicles so you must use...
    view full answer...
  • Converting 4-Way to 5-Way for Boat Trailer on 2022 Hyundai Palisade
    In order to turn your 4-way connection into a 5-way on your 2022 Hyundai Palisade you will not have to install a different wiring harness. What you need is an adapter like the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187. Your existing 4-way will plug into the adapter, and from there you will connect the additional wire to your reverse lights. I have attached a review and installation video for your reference.
    view full answer...
  • Best Way To Add A 5-Way Flat Trailer Connection To My Mototcycle.
    I have a solution for you. However you can use the 4-Pole Hardwire Kit with Circuit Tester # 18252 to add a 4-way flat to your motorcycle. Then using the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187 we can convert it into the 5-way flat that you need. There is not a custom fit wire harness for motorcycles. So you will need the circuit tester to find the correct wires to connect to the universal wire harness. To help I have linked a help article on...
    view full answer...
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Info for this part was:

Employee Lindsey S
Edited by:
Lindsey S
Employee Jameson C
Expert Research:
Jameson C
Employee Adam R
Expert Research:
Adam R
Employee Jacob T
Video Edited:
Jacob T
Employee Dustin K
Video by:
Dustin K
Employee Cole B
Installed by:
Cole B
Employee Wilson B
Updated by:
Wilson B
Employee Kristina F
Updated by:
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Employee Isabelle B
Updated by:
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Employee Amanda M
Written by:
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Employee David F
Test Fit:
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