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Hopkins Wiring Harness with 4-Pole Flat Trailer Connector - Trailer End - 4' Long
Hopkins

Hopkins Wiring Harness with 4-Pole Flat Trailer Connector - Trailer End - 4' Long

Part Number: HM38138
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$5.07
Retail:$5.83
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Trailer Wiring
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Wire your trailer with this universal, splice-in wiring harness so that you can connect the trailer's wiring to your vehicle's during towing. Corrosion-resistant terminals are long-lasting. Meets SAE standards. Great Prices for the best trailer wiring from Hopkins. Hopkins Wiring Harness with 4-Pole Flat Trailer Connector - Trailer End - 4' Long part number HM38138 can be ordered online at etrailer.com or call 1-800-940-8924 for expert service.
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  • Reviews (60)
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  • Videos (1)
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Hopkins Trailer Wiring - HM38138

  • Trailer Connectors
  • Trailer End Connector
  • 4 Flat
  • Plug and Lead
  • 0 - 5 Feet Long
  • Hopkins

Wire your trailer with this universal, splice-in wiring harness so that you can connect the trailer's wiring to your vehicle's during towing. Corrosion-resistant terminals are long-lasting. Meets SAE standards.


Features:

  • 4-Way flat trailer-end connector plugs into the 4-way flat on your vehicle
  • Simple installation
    • Hardwire to existing trailer wiring
  • Corrosion-resistant terminals are long-lasting
  • SAE compliant


Specs:

  • Harness length: 4'
  • Wiring configuration:
    • White: ground wire
    • Yellow: left turn/brake light
    • Green: right turn/brake light
    • Brown: tail lights
  • 90-Day limited warranty


38138 Hopkins 4-Way Flat Connector - Trailer End - 48"

Installation Details HM38138 Installation instructions


California residents: click here


Video of Hopkins Wiring Harness with 4-Pole Flat Trailer Connector - Trailer End - 4' Long

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




Video Transcript for Hopkins Wiring - Trailer Connectors - HM38138 Review

Today we're going to be taking a look at the Hopkins wiring harness with a 4-pole flat trailer end connector. The 4-way flat trailer end connector is going to plug into the connector from your vehicle to power your trailer's signal lights. Pretty simple installation. It's designed to just hard wire to the existing trailer wiring. On the connector portion right here, it's going to feature corrosion-resistant terminals, so these are very long-lasting, and it's got a nice easy-grip design, which allows for simple plugin and disconnect. The overall length of our harness is going to measure about 4 feet long. When it comes to the wiring configuration, you're white wire's going to be your ground.

Your yellow wire's going to be for your left turn brake. Green is for right turning brake, and brown is for your taillights. That's going to do it for today's look at the Hopkins wiring harness with a 4-pole flat trailer end connector.

Customer Satisfaction Score:


Customer Reviews

Hopkins Wiring Harness with 4-Pole Flat Trailer Connector - Trailer End - 4' Long - HM38138

Average Customer Rating:  4.9 out of 5 stars   (60 Customer Reviews)

Wire your trailer with this universal, splice-in wiring harness so that you can connect the trailer's wiring to your vehicle's during towing. Corrosion-resistant terminals are long-lasting. Meets SAE standards.

by:

Perfect! extra long so I got rid of all my bull crab wiring



by:

This replaced a old plug.



by:

Well made, especially the mounding around the plug. Pin alignment was very good.



by:

GREAT PRICE, SERVICE & FAST SHIPPING



by:

Worked perfectly



by:

The wiring harness is cheap and easy. < br>


Hopkins S.

5/11/2017

Thanks for the review on the Hopkins Wiring Harness, Nick! Hopkins appreciates your business.



by:

The Hopkins Wiring Harness was exactly what I needed to repair the trailer. Very affordable.



by:

Great product for the money I had replace my trailer wire at the trailer connector end , the wires are even labeled .



by:

Nice quality wire and connector that is still working well after a good summer worth of use



by:

Parts as described, spare tire and rim for my utility trailer, fast shipping, able to order exactly what I needed, recommend!



by:

Worked as a great replacement for the old/failing plug on my parent's trailer!



by:

Excellent. Fit the factory installed tow vehicle connection perfectly. (F250) Easy to install and worked as it should.



by:

I've only had the products for a couple of days so I can't vouch on quality. Looks good. Doing business with etrailer was a good experience.



by:

Product performs as expected, distributor stand behind products in accordance to need.

Hopkins S.

5/23/2017

Thanks Sam for reviewing the Wiring Harness!! Hopkins appreciates your business.



by:

quality product



by:

Good quality. Fast shipping.

David F.

6/7/2020

still working great



by:

Love all your products. Love how fast you get them out and on the way.



by:

easy to find anything i need , great price and service. no need to go anywhere else,fast delivery.

Hopkins S.

5/31/2017

Thanks Pa John for the great review and rating!! Hopkins appreciates your business.



by:

Fixing the trailer issue.



by:

Exactly what I was hoping for, excellent quality and easy to install. I would definitely purchase again.



by:

real good quality,

Hopkins S.

6/21/2017

Thanks for the review on the Hopkins Trailer Connector, Jim!! Hopkins appreciates your business.



by:

Worked exactly as expected, decent quality wire.



by:

Very pleased. Exactly what I wanted a a very fair price. Shipping was fast. I would definitely order from them again and probably will.



by:

The product was as advertised...good quality at a very reasonable cost.
Delivered expediously.
Thanks



by:

Great support- took the time to go through and explore options. good shipping time as well. I will us i the future Thank You!


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See what our Experts say about this Hopkins Trailer Wiring

  • Does the Blue Ox Tail Light Wiring Kit with Block Diode # BX8811 Come With a 4-Way Connector
    The Blue Ox Tail Light Wiring Kit with Block Diode # BX8811 that you referenced does not come with a 4-Way connector as you stated. To add a 4-Way connector you can simply use the Hopkins Wiring Harness with 4-Pole Flat Trailer Connector # HM38138 and connect it to your current wiring using Butt Connectors # DW05744-5. For a look that is a little more clean and will provide you with a 7-Way to connect to your RV you can use the Hopkins Nite-Glow Tow Bar Extension Cord w/ Socket - Coiled...
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  • 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...
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  • Converting A 5 Wire 4 Way Trailer Connector To Vehicle 4 Way Flat
    It sounds like you have a separated wiring setup with 5 wires - yellow, yellow brown, green, green brown, white. Typically, yellow is left turn / stop, green is right turn / stop, yellow brown is left running light, green brown is right running light, white is ground. You convert this to a standard 4 way by wiring the 5 wires to 4 flat harness # HM38138. This allows you to wire up all of your trailer wires color for color and then simply plug it into the vehicle's 4 way connector. The...
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  • Do 4-Way Connectors Have a Power Wire
    Trailer and vehicle 4-way connectors like you'll find with the 4-Way Flat Trailer Wiring Kit - Vehicle and Trailer Ends # HM48205 do not actually have a hot - or power - wire. As you can see by the cut out I added of the linked help article on trailer wiring (which I highly recommend checking out), a 4-way will activate running lights, brake lights and turn signals. I have added a link to our entire selection of trailer end 4-way connectors for you to take a look at.
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  • Can You Use The 3rd Brake Light Logic Module With A 4-Pole
    For your 2021 Chevrolet Silverado you will have to splice into the factory wiring to use the 3rd Brake Light Logic Module # PP20-702 to connect the left and right turn signals, along with the green wire. You can also combine this harness # PP20-702 with a 4 pole harness like the Hopkins Wiring Harness with 4-Pole Flat Trailer Connector # HM38138.
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  • diagram
    We don't have access to the wiring color diagram unfortunately.
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  • Will Adding 4-Way Wiring To a 2013 Cadillac SRX Risk Damage To The Vehicle?
    On your 2013 Cadillac SRX Luxury you want to use a wiring harness with a powered controlled module like the Curt # C59236. This module uses power from the vehicle battery to operate the lights on a trailer and reduces strain put on the factory wiring. By using a basic 4-Way # HM38138 you put all the additional power load for the trailer on the factory tail light wiring. Since manufactures have switched to using the thinnest wire power to save money this will likely overload the wiring and...
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  • Determining Function of Non-Standard Wire Colors on Trailer to Install 4-Way Connector
    The best way to connect the 4-Way to your trailer wiring is going to be to test each of those wires by applying 12V power to them. By doing this you will be able to see what each wire activates on the trailer to verify their function. Going by wire color alone, as you are seeing, isn't always a good idea because trailer manufacturers or previous owners have a tendency to use non-standard wire colors. Once you determine their functions the trailer wire for left turn/brake light will go...
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  • How to Re-Wire Trailer with 4-Pole Trailer Harness
    A 4-pole trailer wiring harness has three circuits plus a ground, the ground being carried on the white wire. You will just need to test the functions on each trailer wire to confirm how to connect them to a 4-pole pigtail like # HM38138. A junction box # 38656 and ring terminals like # 44-5310A will make it easier to get solid reliable connections. You will want to ground a battery negative terminal to the frame and apply 12V power from the positive terminal to each trailer circuit, one...
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  • 4-Way Trailer Wiring Recommendation that Uses all 16 Gauge Wires
    For a 4-way that has all 16 gauge wire you would want the Wesbar 4-Pole Flat Connector # W787264. The part # HM38138 uses 18 gauge for all wires but the white that uses 16 gauge.
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  • Can Trailer with Brown Yellow and Brown Green Wires Run to Standard 4-Way
    Yes you would be able to use your current trailer wiring configuration with a standard 4-way that only has 4 wires like the # HM38138 that you referenced. Basically the yellow brown and the green brown wire would wire directly to the single brown wire of the 4-way and the other colors would match and you'd be set. What you have now is a wish bone setup that just has a separate wire for the running light circuit for each side of the trailer. We have 4-ways that are setup for this with the...
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  • Availability of Adapter to Go from 4-Pole Round on Trailer to 4-Pole Flat on Vehicle
    I do have a couple options for you, but there isn't an adapter to go from a male (trailer end) 4-pole round to a female (vehicle) 4-pole flat or even a 7-way. So, you could either make your own adapter using part # PK11410 and # HM38138, if you do not want to modify the harness on your magnetic trailer lights, or you could simply replace the 4-pin round connector on them with part # HMC20031, which is going to be the most cost effective.
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  • Tracker Boat Trailer Wires With 7 Wires Connecting Into A 4 Pin Plug
    It could be possible that your 2012 Boat trailer is wired with a wishbone style harness. Similar to Item # A25W2GWB. This type of harness just allows the installer to run each side separate rather than splicing and running extra wires across the bottom of the trailer. Your best bet may be to test each wire function before cutting. You cannot get trailer brakes from a 4 pin connector which is why I am leaning more toward it being a wishbone. Once you determine the proper functions all you...
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  • Troubleshooting Trailer Wiring After Installing Lights And Wiring
    There could be a couple of reasons why the lights are not working now. You said you replaced some lights and wiring. I recommend checking all of the connections to make sure everything is secure and wired properly. You can use a circuit tester like part # PTW2993 to make sure all of the lights and wires are receiving current as designed. If everything checks out the problem is probably the ground connections. Check the inside of the trailer connector for corrosion. If you find any green...
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  • Converting Euro 7-way To Standard 4-Way Flat Trailer Connection
    I am not familiar with the bike rack with lighting, however, you can rewire the 7 pin euro by function to the 4-way flat. I recommend using the Hopkins Wiring Harness with 4-Pole Flat Trailer Connector - Trailer End - 4' Long # HM38138 along with quick splices like # SWC501925-1 or butt connectors like # DW05744-5. The 4-way functions are: White=ground wire Yellow=left turn/brake light Green=right turn/brake light Brown=tail lights I've attached a photo of the Euro functions for you.
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  • How to Connect Thinline LED Trailer Tail Light to 4 pole Connector
    To connect the Thinline LED Trailer Tail Light # STL59RB to your 2017 Kia Sportage's trailer wiring is fairly simple. It sounds like you are going to be mounting the light to a cargo carrier, or other hitch mounted accessory and would like to disconnect it easily when you're not using it. The Hopkins Wiring Harness with 4-Pole Flat Trailer Connector # HM38138 can be wired directly into the light and then plugged into your 4 pole connector. The 4 pole connector is the trailer side, so it...
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  • Parts Needed to Re-Wire European Trailer to RV-Style Trailer Wiring
    Thank you for the photo of your trailer's European wiring. You will be best served by replacing the Euro style connectors on your trailer to the RV-type. We do not offer Euro style wiring harness kits for vehicles. The part you referenced, adapter # 118710, adapts a European vehicle to a 4-pole type connector but does not adapt the trailer to match U.S. wiring. Euro wiring has every function on a separate wire; while here in the U.S. trailer wiring combines the stop and turn signals. The...
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  • What Gauge Wire does 4-Way Trailer Wiring Use
    Typically 4-way wiring consists of 18 and 16 gauge wires. For a 4-way that has all 16 gauge wire you would want the Wesbar 4-Pole Flat Connector # W787264. The part # HM38138 uses 18 gauge for all wires but the white that uses 16 gauge.
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  • Can You Connect the Thinline LED Trailer Tail Light Red Wire to both Green and Yellow Wire
    I believe what my friend Rob was referring to when he said to connect the red wire from your Thinline LED Trailer Tail Light # STL59RB to the yellow and green wires is to connect it to the yellow and green wires of the Hopkins Wiring Harness with 4-Pole Flat Trailer Connector # HM38138. From there you can plug the Hopkins connector into your vehicle wiring harness for power if you are using this on a cargo carrier or other hitch mounted accessory. This process will not harm your vehicle...
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  • Adding A Trailer Hitch Receiver To A 2022 Vanleigh RV Beacon 39FBB 5th Wheel Trailer To Triple Tow
    To know which adjustable width trailer hitch will fit your 2022 Vanleigh RV Beacon 39FBB fifth wheel trailer you'll need to measure the distance between the inside of your frame rails. The Curt Adjustable Width Trailer Hitch Receiver for RVs # C13704 you were looking at fits a frame width of 22" to 66" Wide and has a 5,000lb GTW. If you can get me the frame width for your trailer I can find the correct fit for you. You'll also need a 4-pole connector to transfer your braking and turn...
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  • How To Hardwire A 4-Way Harness On A Small Utility Trailer
    In order to wire a 4-way harness onto your trailer, you will need a few simple items. The first of which will include our Deka Heat Shrink Butt Connector part # DW05744-10 and the Electrical Connector Dielectric Grease part # LT37534. The rest of the tools needed for this install should be fairly common in most toolboxes. Before you install the wires, you will need to strip back a 1/4" of the jacket from each wire and place them into opposite ends of the butt connector. After you have...
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  • Can 4-Pole Wiring Be Submerged Underwater
    4-pole wiring like the Hopkins Wiring Harness with 4-Pole Flat Trailer Connector # HM38138 can technically be submerged underwater but you would want to ensure that the connections are all waterproofed with heat-shrink butt connectors, like # DW05744-10, for the bare wires and some Dielectric Grease # 11755 on the 4-Pole connectors.
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  • Replacing 4-Way Flat Connector With No White Ground Wire Causing Lights To Turn Off
    You are correct that you need a ground wire for your 4-way flat connector. When you are hitting bumps the coupler for the ball has a small amount of play inside which is causing your lights to turn off and on. The Hopkins Wiring Harness # HM38138 will give you a short 4' lead which you can splice into your trailer wiring and run the white wire to a good ground location on the trailer. This will ensure a good solid ground connection for the wiring on the trailer. The Heat Shrink Butt Connectors...
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  • What Does Some Trailer Wiring Have 2 Brown Tail Light Wires
    Common 4-pole trailer wiring like # HM38138 uses one wire, the brown one, for the running lights on both sides of the trailer. Sometimes what is called a 'wishbone' harness is installed on the trailer and this simply uses two separate running light wires - brown with yellow for left and brown with green for right - to make it easier to connect to the trailer lights since that way no jumper wire will be needed to cross from one side to the other. Some examples of wishbone style 4-pole...
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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 Jeffrey L
Expert Research:
Jeffrey L
Employee Cole B
Installed by:
Cole B
Employee Alexander C
Written by:
Alexander C

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