bing tracking image
  1. Trailer Wiring
  2. Custer
  3. Wiring Adapters
  4. Single-Function Adapter
  5. 4 Flat
  6. Plug and Lead
Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat

Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat

Item # ADP001
Our Price: $14.28
Trailer Wiring
Orders above $99 qualify for Free Shipping
Shipping Weight: 0.11 lbs
In Stock
Trailer Wiring ADP001 - Plug and Lead - Custer
zoom in icon
slider vertical icon
zoom out icon
Comment field cannot be left empty.
Name field cannot be left empty.

Thank you! Your comment has been submitted successfully. You should be able to view your question/comment here within a few days.

Error submitting comment. Please try again momentarily.

Product Images

Customer Photos


Need help with installation?
Locate installers near me
This adapter converts a 4-way round connector to a 4-way flat connector. The durable ABS plastic adapter is compact, and pull grips on the flat end make it easy to install and remove. Great Prices for the best trailer wiring from Custer. Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat part number ADP001 can be ordered online at or call 1-800-940-8924 for expert service.
  • All Info
  • Reviews (22)
  • Q & A (0)
  • Videos (1)
  • Photos
  • Why etrailer?

Custer Trailer Wiring - ADP001

  • Wiring Adapters
  • Single-Function Adapter
  • 4 Flat
  • Plug and Lead
  • 4 Round
  • Custer

This adapter converts a 4-way round connector to a 4-way flat connector. The durable ABS plastic adapter is compact, and pull grips on the flat end make it easy to install and remove.


  • Adapter converts a 4-way round trailer connector to a 4-way flat connector
  • Pull grips on flat end make plug easy to install and remove
  • ABS plastic construction is strong and durable
  • Approximate length: 4"

ADP001 Custer Trailer Connector Adaptor - 4-Pole Round to 4-Pole Flat

Video of Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat

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

Video Transcript for Custer Wiring - Wiring Adapters - ADP001 Review

Today we are going to be reviewing Part# ADP001. This is the Custer Trailer Connector Adapter, four-way round to four-way flat. So it's going to convert your round trailer connector to a four-way flat trailer connector. It's got the nice easy-to-use pull grips. It's going to make the plug easy to install and remove. This is going to made from an ABS plastic construction, very strong, durable, and long-lasting.

If we take a measure of the approximate length, measuring from edge to edge, it's going to give us a measurement of about 3-1/2, 3-5/8 of an inch, somewhere right around there. It's really to simple to install. This end right here is going to plug into the four-way round connection on your vehicle. Then, on the back side of that, it's going to expose the connection point for the four-way flat connector. That's going to do it for our review of Part #ADP001. This is the Custer Trailer Connector Adapter, four-way round to four-way flat.


Customer Satisfaction Score:

Customer Reviews

Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat - ADP001

Average Customer Rating:  4.3 out of 5 stars   (22 Customer Reviews)

This adapter converts a 4-way round connector to a 4-way flat connector. The durable ABS plastic adapter is compact, and pull grips on the flat end make it easy to install and remove.


Great product, just what I ordered.
couldn’t find this adapter anywhere else until I came upon it at!!
I have ordered other products from etrailer and have been completely satisfied with those products as well. Thanks.


I purchased a $5 adapter on a Sunday and paid $25 for 2nd day air and didn't get my adapter until Thursday late evening... Sure, I bought from etrailer before and no problems but this sounds like a rip-off. I will sureply accept my shipping money back. 4 business days later is not 2nd day air.


My stock wiring plug receptacle (4Round) on my Fleetwood Motorhome is not wired the same. Could not use it for my application.


This adapts to the "heavy duty" round outlet with one thin and three thick pins (fits my '95 Lazy Daze). Round outlet's lid/latch engages correctly. Flat side relies on friction. Molded housing seems strong and fits snugly.
Note: some descriptions say "length = 4 ft". That should be 4 inches.


The round end will not fix the round socket on the truck. It was made with too large a diameter. Tried to find a socket that it would fit at several auto parts stores and at U-Haul main store and none had one that would fit. Bummer. It's of no use.


Works as shown. It is hard to push into the Pollak socket on the vehicle and seems a little flimsy...have to be gentle with it.


We plugged it in and it works great. Still working great a year later. Very happy with our purchase.


Works as it should/ described. Fast shi pping


Wonderful sight too easily order from with fast fast delivery and great prices! Thank you for this great product


did not fit the female end so I tried to grind it down a little and it is no longer useful - probably would have been ok if it fit


Great product.


Great product, worked just as expected. Thanks


A great product.


just what i needed


Fast service very good




Received. Thank you very much!






See what our Experts say about this Custer Trailer Wiring

  • Availability of 4-Way Round to 4-Way Flat Trailer Connector Adapter
    Sounds like you are looking for the Custer Trailer Connector Adapter part # ADP001 which plugs into a 4-way round and gives a 4-way flat connector.
    view full answer...
  • Which 4 Flat to 4 Pole Round Adapter Has 3 Larger Poles and 1 Smaller Ground Pole Opening
    It looks like you were checking out the Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat # ADP001 which does have the smaller ground pole and the 3 larger poles. This adapter will let you adapt a 4 way flat to fit a 4 pole round and will be the adapter you're looking for.
    view full answer...
  • Availability of 4-Way Round to 4-Way Flat Adapter
    Sounds like what you are in need of is a 4-way round to 4-way flat adapter like part # ADP001. I looked up the Towmate wireless tow lights since we don't carry them and it looks like you can order it with a 4-way round like what you mentioned.
    view full answer...
  • Recommended Adapter for 4-Way Round Trailer Connector on Motorhome
    The Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat # ADP001 will work for your 1995 motorhome with 4-Way round. The 4-Way round trailer wiring connections carry the same functions as the 4-Way flat trailer wiring connections they are just more heavy-duty, so this adapter will allow you to capture the functions you need for your trailer. The pins will fit the dimensions you gave as that is the traditional application for a trailer connector like # PK11404.
    view full answer...
  • Needing a Trailer Wiring Adapter From RV to Flat Towed Vehicle
    If you have a 4-way flat connection on you RV and a 4-way round connection on your flat towed vehicle, then I recommend using a the Custer Trailer Connection Adapter, # ADP001. This adapter used with a wiring harness like # 18045 will allow you to connect to the 4-way flat connector on your RV to the 4-way round connector that is installed on your flat towed vehicle.
    view full answer...
  • Adding a 4-Pole Harness to a 2013 Audi Q7 with a Factory 7-Way
    It sounds like you're trying to install a standard 4-pole on your vehicle. To add a 4-pole to the factory 7-way on your 2013 Audi Q7, you can use the Hopkins Plug-In Simple Wiring Harness, part # 41155. This will connect into your 7-way and give you the 4-pole you need. I've linked to a video installation of this harness on a 2018 Dodge Durango so you can see how it works. However, if you have a 4-way round on your trailer, then you can use two adapters to get it to hook up to your 7-way...
    view full answer...
  • Best Way to Convert a 4-Way Round into a 7-Way RV Harness
    It sounds like you have a 4-way round connector and are needing an upgrade to a 7-way connector. You are correct in looking at the etrailer Universal Installation Kit, part # ETBC7, as the best way to get the 7-way. As for the splicing and wiring into your 4-way round, if you'd rather not do that, we do have an additional adapter that you can use to simplify things. It's the Custer Trailer Connector Adapter, part # ADP001. This easily converts your 4-way round into the 4-way flat that...
    view full answer...
  • Pin Locations On 4-Way Round and Flat Connectors
    I have included a picture below that will tell you which wire goes where on a 4-Pin Round Vehicle Connector # PK11410. This will allow you to see what each pin is for the 4-Way Flat to Round Adapter # ADP001 that you already have.
    view full answer...
    Image 1 for Image 2 for
  • 4-Way Flat Adapter Recommendation to Use with RoadMaster 4-Wire Connector # RM-910030-1
    Yes, the 4-way round to flat adapter part # ADP001 that you referenced will work with the RoadMaster 4-Wire Connector # RM-910030-1. It will plug right in and give you a 4-way flat to use.
    view full answer...
  • Wiring Adapter to Mate 4-Pole Flat Vehicle Connector to 4-Pole Round
    The easiest and least-costly solution for mating your wiring connectors is to replace the connector on your portable lights with a trailer-side 4-pole like # HM48110. This will allow your lights to be connected to the 4-pole on your vehicle. If you need to convert a 4-flat to a round 4-pole you can use either # ADP001 or # 47465. I have linked our main page for wiring adapters and you can use the filters on the page to select each type of connector you need to see available adapters....
    view full answer...
  • Trailer Wiring Adapter to Convert 4-Pin Round Vehicle Connector to 4-Pole Flat Type
    Thank you for providing the photo of the 4-pin round trailer connector on your vehicle. We do have two different products that will adapt this connector to a standard 4-pole flat trailer connector. Hopkins offers their adapter # 47465 (that can be used with mounting bracket # 18144) and Custer offers their adapter # ADP001 that does not require a mounting bracket.
    view full answer...
    Image 1 for
  • Different 4-Way Connector Styles and Adapters
    There are not two different 4-pin round connectors; there are just two types of 4-pin connectors, 4-flat such as the Hopkins Endurance 4-Way Flat Trailer Connector # HM48110 and 4-round such as the Pollak Heavy-Duty, 4-Pole, Round Pin Trailer Wiring Connector # PK11402. The 4-round is more rare than 4-flat so you are less likely to see it. If you have a 4-round on your vehicle you can use the Trailer Connector Adapter - 4-Way Round to 4-Way Flat # ADP001. I have also added a link to a...
    view full answer...
    Image 1 for
  • Solution for 4-Way Round Connector on Trailer to 4-Way Flat Connector on 2016 Honda Pilot
    I do have a solution for you but unfortunately there are no adapters for a round 4-Way connector on your trailer to the Curt T-Connector # C56291 on your 2016 Honda Pilot. Instead what you will need to do is swap out the 4-Way round connector on your trailer for a 4-Way flat connector. I recommend cutting the connector off and splicing the Hopkins Endurance Easy-Pull Harness # HM38134 on your trailer wiring so that you get a connector on your trailer that is compatible with your vehicle....
    view full answer...
  • What Style 4-Way Round Socket Does the Custer Trailer Connector Adapter # ADP001 Fit
    The Custer Trailer Connector Adapter # ADP001 that you referenced is designed to fit 4-way round receptacles like the Pollak Heavy-Duty, 4-Pole, Round Pin Trailer Wiring Socket # PK11404.
    view full answer...
  • Solution for 4-Way Adapter With 4-Way Flat Male End and 4-Way Round Male End
    Your typical 4-way flat to round adapter like the # ADP001 is the opposite of what you need on both ends. Although nobody makes an adapter like this, you can easily make your own. For the 4-way flat trailer end connection you can use the Hopkins Wiring Harness with 4-Pole Flat Trailer Connector - Trailer End - 4' Long # HM38138. You can cut the wiring harness down if you want it to be shorter but this gives you a decent amount of wire to work with. Then you will need the RoadMaster 4-Wire...
    view full answer...
    Image 1 for
  • 4-Way Flat to 4-Way Round Trailer Plug Wiring
    It may seem odd to clarify, but we sometimes have customers describe things differently than we may. So if you are looking for the connector between a 4-way flat on your vehicle and the 4-way round connector a towed vehicle would plug into you simply would need the Custer Trailer Connector Adapter - 4-Way Round to 4-Way Flat # ADP001. If you needed a longer connector you can use # Adapter 4 Round to 4 Flat # 47465. If you are looking for a long trailer wiring umbilical cord, you would...
    view full answer...
    Image 1 for Image 2 for
  • Recommended 4-Way Connection Between Towed Vehicle and Motorhome
    The only real advantage of the 4 round over the 4 flat trailer connector is the clean look of the connection point and the protection from elements when not in use. For instance the Pollak Heavy-Duty, 4-Pole, Round Pin Socket, Concealed Terminals - Chrome - Vehicle End # PK11410 has a clean finished look on the front of a towed vehicle and will protect the connection from dirt and debris with the spring loaded cover. Many people like the connection between the motorhome using a harness...
    view full answer...

Do you have a question about this Trailer Wiring?

  • Why

    At we guarantee:
  • Real product know-how.

    We make sure that the products we sell are what we say they are, and that they work the way they are supposed to work. Get real advice from a real person who has the knowledge and expertise needed to solve your problem.
  • Most detailed, accurate trailer wiring information available.

    Because we take providing accurate product information seriously, we take our own detailed product photos, demo videos and installation videos, as well as verify measurements, instructions, and vehicle fit information.
  • Installations, made easy.

    We love helping people and have the most highly-trained customer service, hands-on experience, step by step videos and installation instructions.
  • Fast shipping.

    Your order is automatically routed to get out of our warehouse and to your door as quickly as possible. Receive free shipping on orders over $99.
  • Personalized service for life.

    We provide one-on-one, personalized service from the ordering process through the life of your product.
  • Trusted since 1946.

    We've been serving customers since our parts store first opened in 1946 and continue to be recognized by our customers, our vendors and third parties for exceptional service.
  • Returns Policy

    Need to return an item? No problem. Please read our Returns Policy for more information.

Info for this part was:

Employee Jameson C
Expert Research:
Jameson C
Employee Rachelle B
Written by:
Rachelle B

At we provide the best information available about the products we sell. We take the quality of our information seriously so that you can get the right part the first time. Let us know if anything is missing or if you have any questions.

Product Experts Available Now!
Call 1-800-940-8924