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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
Our Price: $10.35
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Trailer Wiring
Shipping Weight: 0.23 lbs
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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. Great 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 1-800-940-8924 for expert service.
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  • Reviews (83)
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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

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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 4-Way Flat to 5-Way Flat Trailer Connector Adapter Installation - 2010 Acura MDX

Today on our 2010 Acura MDX we're gonna be installing Curt's four way flat to five way flat trailer wiring adaptor. This adapter's gonna allow you to take your four pole wiring on your MDX, and convert it to five pole wiring. Five pole wiring is a lot less common than your four pole wiring, so you typically don't find kits out there that just install straight five pole wiring. But if you're trailer does have a five pole, and you need this simply plugs in. And to get those reverse lights working you can take blue wire and route it your reverse lamp circuits on your vehicle. It comes with wiring, and quick splice to get that connected.We'll begin our installation at the back of the vehicle with the lift gate open.

We'll need to connect the reverse lamp circuit wire. Now the one that comes with your kit isn't gonna be long enough to reach your connector, so we're gonna have to extend this. You can pick up additional wire here at We'll access our reverse lamp circuit located behind the grommet here in the upper left behind our lift gate. You just wanna take that, and pull that back to reveal our wiring.And we want the small brown wire that's in here.

This is gonna be our reverse lamp circuit. Now that we've got our brown wire separated from the rest of wiring we'll slide the quick splice that comes with the kit over the brown wire. Just like that. We'll take our new wire, slide it into the other end of our quick splice there, and then use a pair of pliers or channel locks to crush the splice down into the wires. After you've got it crimped down just close your plastic in there, and we can reinstall our grommet.It's not a bad idea to maybe poke a hole in here, and you can feed that wire out through that hole.

So, we're just gonna take a small screw driver here. Try and stay towards the bottom. Poke a hole through it with our screwdriver then we'll take the other end of our wire and we're gonna poke that from the inside out through that hole. And you can further seal that up with a little bit of black silicone. If you need some silicone you can pick some up here at can then take our wiring, we're gonna route it down to our four pole connector where ever you have that mounted.

Our customer has his mounted outside the vehicle, so that's where we're gonna be routing it. If yours was inside the vehicle then you could simply come down and just wrap it around the weather stripping down here below. Once you get about that far I'm just gonna pull back the weather stripping, and we're just gonna follow the weather stripping down. Now if you're going outside we're gonna keep following that weather stripping down bringing our wiring along the way until we get about here where we can go down through the open seam underneath our weather stripping. And here you can just reach up behind the bumper, grab that wiring, and pull it down. Then you can just push the weather stripping back into place. If it does get up above your panel here you can kind of pop that up, get it tucked back under.Now we're under our vehicle. We've got our wire that we ran down. We can go ahead and trim off any excess that we've got there. Want to make sure we got some so we can connect it to our blue wire here, so we're just gonna trim that up about there. Now we'll take our blue wire, we're gonna strip it back. We'll take the wire that we ran down, we're gonna strip it back as well. And now we'll crimp the two together. Now you're kit doesn't come with any crimps. We're using a Heat Shrink Butt Connector for ours. And again our customer has his wiring routed outside the vehicle where typically on your MDX it's gonna be inside. If it was inside the vehicle you likely wouldn't need to extend the wire longer like we did. So, then we'll just crimp the other end on to our white wire, and then we can heat shrink it down.Now we can take the excess, we're gonna zip tie that to our four pole wiring. No zip ties come with your adaptor, but you can pick some up here at Now everything's all connected, and all we need to do is plug our four pole end into our four pole flat on our vehicle, and plug our additional circuit in right there. And you're ready to now plug up to your five pole connector on your trailer, and hit the road.Now we can test everything out. You can either plug this into your trailer to test it out, or you can use a test light like the one I have here. So, we're gonna hook our ground up to the exposed terminal there coming out of our connector. I've got the hazard lights turned on as well as the headlights, and that'll be able to check all of our circuits except for the additional one that we ran which is for our reverse lights. You should have on your brown wire a taillight circuit that'll come up solid. Our yellow and green wires are our left and right turns signals, so they should be flashing with our hazards. These also double as your brakes. And lastly we have this one here, we'll have to put the vehicle in reverse in order to test that. So, you may need some extra assistance because you don't want to be back at the back of the vehicle when it's in reverse with nobody inside. And you can see our reverse lights are working properly.And that completes our installation of Curt's four way flat to five way flat trailer adaptor on our 2010 Acura MDX.

Customer Satisfaction Score:

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   (83 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.


Used my 4-5 pin adapter to tow my 20 foot Mako to the ramp here in East Boothbay this past weekend. I am always pleased with the wide array of products etrailer stocks that help keep me on the road.


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%.



Still 100 satisfied a year later. Great product and company customer service is commendable.


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.


Delivered fast and efficiently. Thank y ou.


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.

Barry B.


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.


Just what he said I needed
Will recommend
to all


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.

Etrailer Expert

Mike L.


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.


Really fast turn around time after ordering product. Thanks


Quick install, highly recommend the ada pter.


Arrived as ordered and in a very timely manner


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.


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


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.


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.


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.


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!!


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

Hugh H.


Works perfectly. I like its tight fit for a great conection


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!


Product as specified on eTrailer site to solve a particular problem between my car and a boat trailer. Excellent description and instructions.


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

Leonard E.


Still working as well as it did on day one. 5 star product.


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


Thank you for world class service. You instantly fixed a problem I was hanging for two weeks. I really do appreciate you.


Products were exactly as described and work great. Had all the accessories I needed and showed up on time. Also came with detailed instructions on how to install! Will.use them again.


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.


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

Show More Reviews

See what our Experts say about this CURT Trailer Wiring

  • 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...
  • 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...
  • How To Adapt Your 4-Pole Flat Trailer Connecter To A 5-Pole Flat Trailer Connector
    Yes, I recommend the Curt Trailer Connector Adapter # C57187. This adapter will connect to the 4-pole connector you have on the rear of your vehicle and includes an extra wire to run to the reverse light circuit on your vehicle. The reverse light wire will come with a bullet-connector so that you can remove the adapter as needed. I've attached a short video below where Dave will show you how to splice in the reverse light wire.
    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...
  • 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...
  • 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...
  • Part Needed to Convert 4-Way to 5-Way On Ford Super Duty
    There is not a plug-in adapter; you'll need to splice into the reverse light wire on your Ford Super Duty. The correct part for that is the following: - Tow Ready 4 Pole to 5 Pole Trailer Wiring Adapter # 20036
    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...
  • 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...
  • 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...
  • 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...
  • 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...
  • 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...
  • 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...
  • 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...
  • Recommended 5-Way Adapter for a 2017 Honda Pilot
    You don't need a new harness. All you need to add a 5-way to your 2017 Honda Pilot is the Curt Trailer Connector Adapter item # C57187. You will plug the adapter into the existing 4-Way on your Pilot. Then the blue wire will get spliced into the reverse circuit wire on your Honda for the reverse lockout on the boat trailer to function. I have linked a installation video we did below so you can see the steps on how to get the adapter set up. This video isn't on a Pilot but the part is universal...
    view full answer...
  • How To Get A 5-pole Trailer Wire Harness For A 2019 Jeep Grand Cherokee
    To connect to the 5-pole connector on your trailer you would to install a 4-pole wire harness first and then use an adapter to get the reverse light signal for your surge brake override. For a 2019 Jeep Grand Cherokee you would want to use the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118727. This wiring harness has plug-in connectors for easy installation and will allow you to then plug-in an adapter like the Curt Trailer Connector Adapter # C57187. The blue wire...
    view full answer...
  • What Is The Purpose Of The 5 Flat Trailer Wiring Harness On A Vehicle?
    I will start off by saying that the white wire most definitely needs to be grounded. I always recommend doing this directly to the frame of your vehicle as it has the most metal. This is almost 100% the cause for your lights not currently working. Typically the 5 Flat, like the Curt # C57187, is added to a 4 Flat when someone is pulling a boat trailer with a surge style brake actuator that has electric reverse lockout. The 5th port will be attached to reverse lights and will send power...
    view full answer...
  • Parts Needed to Install 4 way and 5 way Plugs on 2019 Jeep Wrangler Unlimited
    We've got just what you're looking for. You can use the Curt # C56407 to install the 4 way connector on your 2019 Jeep Wrangler Sahara Unlimited, which will give you the 4 way connector. You'll then need to install the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End # C57187, which can be plugged in when you need to tow the trailer with a 5 way connector. This will plug into the C56407 you've installed and add a connection to the reverse light circuit that will...
    view full answer...
  • Recommended 4-Way Connector for a 2020 Honda Pilot
    The Curt T-Connector Vehicle Wiring Harness item # C56291 is going to be the best option to add a custom fit connector to your 2020 Pilot. This plugs into existing wiring in your rear cargo area. It will provide you with a 4-flat connector. If your boat trailer has a 5-way connector you will also need the Curt Trailer Connector Adapter item # C57187. I have linked a couple of installation videos below so you can see how to get these parts set up.
    view full answer...
  • Troubleshooting No Turn Signal Wiring on Trailer When Connected to New 2020 Nissan Frontier
    Nissan is notorious for botching up on the wiring front so I definitely get where you're coming from. If the U-Haul trailer has more than one turn signal on the side that wasn't working and it's just one light then it sounds like that light itself either has bad wiring, a bad bulb, or it just needs to be replaced altogether. If there is just one turn signal on that side the above can be true, but your 2020 Nissan Frontier also may need just a new relay for that specific turn signal, which...
    view full answer...
  • Wiring Harness for a 2021 Toyota RAV4 Prime
    I just spoke with my rep at Curt and he told me you do not need to purchase a wiring harness that is specific to the 2021 Toyota RAV 4 Prime model. He said that the Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector item # C56434 will fit your RAV4 Prime. To get a 5-Flat connector you will need the Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat item # C57187.
    view full answer...
  • Connecting Vehicle Side 4-Way to 5-Way on 2003 Boatmate Trailer
    Based on your description it sounds like your 2003 Boatmate trailer has hydraulic drum brakes with an electric lockout on the surge brake actuator. If you had electric brakes the trailer connector would likely be a 7-way, and a 5-way flat would not be able to power the brakes. You are correct though, the 5th function is for the reverse light circuit. When you put your vehicle in reverse this sends power to the lockout so the surge brakes do not activate and lock up in reverse. In order...
    view full answer...
  • How To Install a 5-Way Trailer Wiring Harness on a 2019 Honda Pilot for a Boat Trailer
    They do not offer a direct plug and play 5-way trailer wiring harness for your 2019 Honda Pilot or most vehicles for that matter nowadays. The only way to obtain a 5-way trailer wiring harness is to use a 4-way trailer wiring harness, the Curt T-Connector Vehicle Wiring Harness part # C56291 and then a 4 to 5-way adapter, the Curt Trailer Connector Adapter part # C57187 which only requires one splice on the vehicle and trailer. The reverse light circuit on your Pilot should a brown wire...
    view full answer...

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Info for this part was:

Employee Lindsey S
Edited by:
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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:
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Employee Cole B
Installed by:
Cole B
Employee Wilson B
Updated by:
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Employee Kristina F
Updated by:
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Employee Isabelle B
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Employee Amanda M
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Employee David F
Test Fit:
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