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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Curt Trailer Connector Adapter - 4-Way Flat to 5-Way Flat - Vehicle End Single-Function Adapter C57187
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  • Wiring Adapters
  • Single-Function Adapter
  • 5 Flat
  • 4 Flat
  • Plug and Lead
  • 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. Lowest Prices for the best 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 800-298-8924 for expert service.

  • All Info
  • Reviews (14)
  • Q & A (28)
  • Videos (2)
  • Photos
  • Why etrailer?

Curt Wiring - C57187

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:  4.6 out of 5 stars   (14 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.

- C57187

Quick install, highly recommend the ada pter. 628248

- C57187

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. 691231

- C57187

Perfect part and quick shipping! 690700

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It came quickly and was exactly what I needed for a great price. 687056

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E trailer 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. 666756

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Excellent product 662976

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It was easy to determine what product that I needed because of the video associated with the produce. My order came quickly and was the exact one I ordered. 661395

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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!! 650400

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Works 599458

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YOU GUYS ARE THE BEST..............Easy to deal with and reliable! Thanks! 574353

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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! 571734

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great !!! 563852

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Ordered Monday night and here Thursday before I needed it! No auto part stores in my area had what I was looking for but these guys sure did. Thanks! 549334

- C57187

Product as specified on eTrailer site to solve a particular problem between my car and a boat trailer. Excellent description and instructions. 509831

- C57187

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. 508250


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.

-- Mike L - 05/15/2018


Ask the Experts about this Curt Wiring

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  • Part Needed to Convert 4-Pole Wiring Harness to 5-Pole Flat Connector Format
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  • How To Wire a 4-Way On a Motorcycle Trailer With a 6-Way
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  • How To Install a 4-Way Trailer Connector on a 2016 Buick Enclave
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  • How to Install a 5-Way Trailer Connector on a 2003 BMW X5
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  • What Causes a Trailer With Surge Brakes To Lockup While In Reverse
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  • Solution to Allow Motorcycle with 5-Way to Tow Trailer with 4-Way
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  • How To Install a 5-Way Trailer Wiring Harness on a 2019 Honda Pilot for a Boat Trailer
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  • How to Use the Lockout on the Titan Brake Actuator with Manual Lockout Part # T4500600
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  • Trailer Lights Do Not Work and Brakes Lock Up in Reverse
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  • How to Activate Trailer Reverse Lockout with Vehicle that Has Only 4-Way
  • You'd need to convert the 4-way to a 5-way so that you can have the reverse light circuit for the lockout solenoid. For that you'd want the part # C57187. Basically this just plugs into your vehicle 4-way and then you run the extra wire to your reverse light circuit using the included quick splice and you're ready to go.
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  • How to Wire a Motorcycle Trailer To Be Towed With 4-Way Trailer Connector
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  • Troubleshooting No Power at Turn Signal Pins After Installing Curt 4-Way to 5-Way Adapter
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  • How to Attach a Motorcycle Trailer with 5-Way to Vehicle with 4-Way
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Info for this part was:

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

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