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Adapter 4-Pole to 7-Pole and 4-Pole

Adapter 4-Pole to 7-Pole and 4-Pole

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Hopkins Wiring Adapters - 37185
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Adapter converts from 4 pole wiring on vehicle to 7-pole round plug and 4-pole flat. Additional wire leads for brake, power and accessory. Lowest Prices for the best trailer wiring from Hopkins. Adapter 4-Pole to 7-Pole and 4-Pole part number 37185 can be ordered online at or call 1-800-940-8924 for expert service.
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Hopkins Trailer Wiring

  • Wiring Adapters
  • Multi-Function Adapter
  • 4 Flat
  • 7 Round - Blade
  • Plug and Lead
  • 4 Flat
  • Hopkins

Adapter converts from 4 pole wiring on vehicle to 7-pole round plug and 4-pole flat. Additional wire leads for brake, power and accessory.


  • Adapter converts from 4-pole wiring on your vehicle to 7-pole round plug and 4-pole flat wiring for trailer side
  • Adds additional wire leads for brakes, power, and accessory wiring
  • Wire functions:
    • White - ground
    • Blue - brake
    • Black - hot lead - 12 volt power supply
    • Purple - auxiliary
  • Mounting bracket included


  • Connector measures 3" x 3"
  • Distance between vehicle mounting holes: 2-3/16"
  • 90-Day limited warranty

product detail

Wire Functions:
White: Ground
Blue: Brake
Black: "Hot" Lead - 12V power supply
Purple: Aux. - Reverse Lights etc.

Note: If you run the hot lead (black wire), you will need a circuit breaker, for example 9510 (sold separately), between the adapter and the battery itself.

47185B Adapter 4-Pole to 7-Pole and 4-Pole - Hopkins # 47185B, TAP # 37185

Item # 37185

California residents: click here

Customer Reviews

Adapter 4-Pole to 7-Pole and 4-Pole - 37185

Average Customer Rating:  4.8 out of 5 stars   (549 Customer Reviews)

Adapter converts from 4 pole wiring on vehicle to 7-pole round plug and 4-pole flat. Additional wire leads for brake, power and accessory.


Working fine one year after being installed! Towing a Bushwhacker, I had to draw a wire to the battery for operating the camper electric brakes, and added a Curt Echo bluetooth brake controller.


Your information on how to connect to controller wasted a lot of time on the adapter under the steering column. In my Ford Expedition, the existing connector was plugged in and Brown not Gray. It was a simple swap. Instead, I tore apart panels under dash looking for an unconnected gray plug. Also you should sell the proper adapter for the rear end connector also. A simple plug swap vs. cutting 2 wires on Ford's wiring harness wires and using butt connectors would save so much time. Also, having a long purple wire for backup lights (not used very often) and short leads for hot and electric brakes was really stupid. I had to add 1 ft of wire to each - more butt connectors and potential for failure.

It is unusual that the 21 Ford Expedition will come with an adapter that is already plugged in under the dash to the left of the steering column. We do have listed as a tech tip for part # 37185
Adapter 4-Pole to 7-Pole and 4-Pole
that an additional length of wire may be necessary to connect the 7-Way socket of part 37185 to the vehicles tow package wires which are along the rear frame rail.
-- Etrailer Expert Jenny N - 02/28/2022


This was exactly what I was looking for to add to my 2017 Ford Expedition! It is an easy to install plug-n-play product to convert a factory 4-pin connector to a 4/7-pin connector.

I plugged the 4-pin in, connected the brake wire, and grounded it. Ignoring the auxiliary + power cables, everything worked on the first test. The 4-pin connection was given some dielectric and wrapped with electrical tape to keep it sealed from the elements, and the slack was zip tied to secure it.

I still need to give it some finishing touches (fill the bracket gap with some black silicone, maybe find the reverse and/or power lines), but it lets me haul my camper!


2018 wrangler unlimited Sport S. Without trailer wiring. Completed installation today. Used a 4 flat along with a 7 pin converter. Works and fit perfectly. Very hot day and work slowly and carefully. Very satisfied . Great folks at etrailer. Great products, great quality and prices. I'm a several time repeat customer and couldn't be more satisfied.
4 pin harness Was a 56407 and the 7 pin adapter was a 37185.


Really great, I needed this 7 pole to connect my High Camp teardrop to my 2014 BMW X3 and the 4 pole for a small utility trailer. They both work beautifully


The connector is standing up well for it's intended purpose. Easy to install.


Installed on a 2010 Ridgeline. Just what I needed at a great price. Install was a breeze. etrailer is the best place to find all the stuff that auto dealers rip you for. Good quality and the customer service is above reproach.


Nice quality adapter harness. I would highly recommend


The product itself is very well made. The 4-pin connector is molded into the product and very sturdy. The 7-pin connector is held closed by a spring and has a foam gasket to keep water out. The 4-pin wiring is only about a foot long, and the additional 7-pin wiring is a bit longer. I do not have a brake controller (but do borrow a trailer with the 7-pin wiring), so I removed those wires. I also hard-wired all the connections, so I can't speak to the quality of the 4-pin vehicle connector.

The mounting bracket is thin steel, which worked well for me, as I had to bend the mounting plate to make it work for my installation. The paint on the mounting plate appears to be high quality as I bent the plate and banged it around quite a bit during install and did not nick the paint. The plate is drilled so that is can be mounted with the 7-pin hinge facing up, down, left or right.

The hardware is zinc coated, so it should hold up well to the weather. I went ahead and replaced it with SS to make sure. I also replaced the standard nuts with SS nylon lock nuts to make sure nothing would back out due to vibration. If you plan on using the supplied hardware, I would strongly suggest Loctite on the mounting nuts.

I installed this on a CX-5 with hitch # 87623, wiring adapter # C56011 and hitch cover # I-728. Over all a very clean installation. The connector is completely hidden inside the bumper, but easily accessible.


It was pretty straight forward at installing and does what it’s need to do.

It is still working strong. When something works you don’t give it much thought.
Weston - 04/22/2022


AWESOME hitch unit. Strong, very easy to install (went in like a dream in 30 minutes), heavy duty, and right after I installed it on my 2011 Ford F-150 SuperCab I immediately towed a trailer with a 1971 MGB on it from North Carolina to Connecticut.

Awesome Hitch unit! Very strong and useful hitch unit. I dont even know it is on the truck until I need it. Wish I had purchased and installed this years ago, instead of trying to use the hitch ball installed on the bumper itself.
Jason M - 11/14/2021


Installed on our 2019 Edge ST with no significant issues. Works as expected, has reasonable required depth behind connector for ease of install, and the bracket was quite adaptable after some bending and cutting. Not impressed with the overall feel, though - plastic seems lightweight and cover hinge pin is already rusting after two winter weeks in western PA. Long term durability tbd.


Very well made and fit bracket good


This worked as expected. Perfect fit for my application


Pretty easy to install and works as expected. The model in the video is a little different - the hole pattern is not quite the same. But the video was still useful.


I recently installed the 4-pole to 7-pole adapter on my 2015 Highlander. My first install worked OK, but I ran into a ground clearance issue using the original mounting location. Etrailer suggested using a 2 1/2" mounting box to relocated the connector. Part number 18156 worked perfectly.


Wow after Charles great advice this was so simple to install, [online] video was point on and the hardest thing was finding the reverse wire.
Thanks so much for a good product and excellent advice, here is the pic after install!




The trailer wiring adapter was perfect and shipped in no time. Looks great on my ford ranger. Im very happy.
Was 4 flat only and now I can light my 7 way 18' trailer and have the capacity to add a brake controller (which I will add)


2012 Chevrolet Express..Looks and works great! Easy install..2 1/8" hole saw for center, 3/16" drill bit for mounting screws. Thank you etrailer!


Prompt delivery and works great.


Well made and versatile.


Just what I need to tow an RV trailer. Also has a four flat connector. Very easy to install on the 18136 bracket.


Lacking instructions


everything good, we use etrailer for all our trailer needs

Show More Reviews

See what our Experts say about this Hopkins Trailer Wiring

  • Trailer Brake Controller Comes on Full Power with Head Lights on a 1999 Chevy Silverado
    I know exactly what is wrong. The red wire on the brake controller harness plugged into your 1999 Chevy Silverado is in the wrong location in its plug. This is a common issue. All you have to do is move the red wire to the correct location. I have included a picture showing how the various wires should be configured in the end that plugs into the truck.
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  • The Function of the Auxiliary 12-Volt Connection on the 7-Way Trailer Connection
    The auxiliary 12-volt wire that runs from the 7-way connection to 7-way trailer plug will supply 12-volt power from the vehicle to the trailer. The 12 -volt power will allow interior or exterior lights to run that are not wired in to the trailer's tail and clearance lights. The light will operate separate from the trailer clearance and tail lights and will not need to have the truck light turned on to work. The auxiliary wire will also allow you to use other 12-volt trailer accessories,...
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  • Parallel Batteries Versus Batteries Wired in Series
    If two batteries are wired in parallel, the positive terminals of each battery will be connected together, as will the negative terminals. Assuming both batteries are 12 volt, you'll have a 12 volt output but there will be more capacity. If the batteries are wired in series, the positive terminal of one battery will be connected to the negative terminal of the other. This would double the output of the batteries, assuming each battery is a 12 volt, wiring the batteries in series would...
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  • Adding a 4- and 7-Way Trailer Connector to a 2003 Ford F-150 with 4- and 5-Way Connectors
    You won't have to replace all the wiring on your 2003 Ford F-250 to install a 7 and 4-Way connector. All you will need is # 37185. The 4-Way you have will plug into the 37185 (the 4-Way functions are retained). Then ground the white wire to the truck frame. To wire in the remaining wires you will first trace your 4-Way wiring forward under the truck where it plugs into another harness. Inside this harness there will be an orange wire and a blue wire. The orange wire will go to the 37185...
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  • Adapter 4-Pole to 7-Pole and 4-Pole For Tow Vehicle With 4-Way and Trailer With 7-Way
    Harv, The Hopkins Adapter part # 37185 4-Pole to 7-Pole and 4-Pole is exactly what you need to adapt the 4-way to the trailer's 7-way connector. Plug the existing 4-way into the pigtail from the 7-way plug and then ground the 7-way plug. The trailer connector will plug into the 7-way but the only functions that will work is the trailer lights which sounds like all you need.
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  • Where Are the Blue Brake Controller and Battery Charge Wires Ran On a 2006 Ford F-150 for a 7-Way
    The brake output wire as well as the trailer battery charge wire are already ran for you from the front of the vehicle to the rear of the vehicle. That said, if your truck did not come with a factory 7-way then you still need to attach these two wires to the 7-way. For a 7-way, I recommend the Adapter 4-Pole to 7-Pole and 4-Pole part # 37185. If you take a look at the attached photo you will see where the wires end and once cut loose from the harness can be run to the above 7-way.
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  • 7-Way Adapter for 2018 Ford F-150 with Factory 4-Way
    Yes, the 4-way to 7-way adapter part # 37185 that you referenced does fit your 2018 Ford F-150 that has a 4-way on it currently. If you need to activate either the brake controller or 12 volt accessory wire circuit of the 7-way the wiring is present at a wiring harness near the rear of the truck on the frame rail as well like what you can see in the attached picture.
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  • How Does 4-Way to 7-Way Adapter # 37185 Install If Trailer Brakes aren't Needed
    All you'll need to do is connect the 4-way of your 2015 Ford Edge to the 4-way of the # 37185, ground the white wire, and you'll be set! All of the trailer taillight circuits will be active and you can just tape up the extra wires not needed.
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  • Determining How Many 6V Batteries Are Needed for Camping Trip
    Determining if using four 6V batteries will be overkill is really going to depend on a few things specific to your application. Factors such as the planned length of your trips, the amount of appliances (along with their amp draw) you will need to have powered, the need for larger appliances like an Ac, etc will all play a part in deciding just how much power you need. Four batteries will essentially double your amp hours (when compared to two). You will really just need to find out the...
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  • Why Would Vehicle Fuse Blow After Installing Trailer Battery
    What fuse blew when you connected the battery? Most likely what happened is that there's a short somewhere on the 12 volt accessory circuit near where you wired in the battery since it happened after the battery install. I'd recommend going over the trailer area looking for any obvious signs of a short and fix as needed.
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  • Troubleshooting Brake Controller Losing Connection with Running Lights Activated
    It definitely sounds like there is a ground issue somewhere on your Ford F-150 or trailer. A weak ground will usually show itself when additional power draw is put on the system, such as in your case when activating the running lights on top of the signal lights and brake output signal. I recommend making sure your ground connections on the trailer are secured to clean, bare metal surfaces. You can check the ground wires from the brake assemblies as well. You may want to try and move...
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  • How to Wire 4 12 Volt Batteries to a Motorhome
    There are two different ways that you can attach the four 12 volt batteries to your 1983 Blue Bird Wanderlodge. You can attach them in series or parallel. Attaching the batteries in series will increase your power output. Attaching the batteries in parallel will keep power output the same but increase the capacity. The best way to wire them is all going to depend on how you use them. However, I recommend wiring them in parallel so you do not end up with a 48 volt system that would be difficult...
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  • Availability of Replacement 7-Way Connector that Comes with ETBC7
    Best option would be the part # 37185 which will give you a replacement 7 and 4-way adapter like you need. This is the same as what comes with the # ETBC7. We don't have a version of this that is metal.
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  • Where are the Blunt Cut Trailer Brake and 12 Volt Power Wires on a 2011 Toyota Tundra
    In order to find the brake output (usually blue) and 12 volt power (usually black) wires on your 2011 Toyota Tundra you will need to follow the wires that lead to the 4-way trailer connector back towards the cab while testing them with a circuit tester like part # ALL640595 until you find the correct circuits. The trailer connector you need to add the 7-way is the Adapter 4-Pole to 7-Pole and 4-Pole part # 37185 which plug into the 4-way you have now and contains the blunt cut ends for...
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  • Does 12 Volt Accessory Circuit of 7-Way Have to Activate for Brake Controller
    It is not needed to wire up the 12 volt power circuit of a 7-way to use trailer brakes. Those two circuits are totally separate. If you don't have a need for a 12 volt accessory circuit you would not need to activate it and the controller will work just fine.
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  • How to Determine if Battery Bank on 5th Wheel Trailer is Wired in Series or Parallel
    That depends on how the batteries are wired. If the battteries are wired in series like I believe they are that would mean you have two 6 volt batteries wired in a way that makes the output 12 volts. If they were wire in parallel it would be to 12 volt batteries wired so that the output is 12 volts. Check out the picture I attached that shows how the different style of battery wiring look to compare to what you have.
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  • How to Wire 2 New Batteries to a 1993 Holiday Rambler 5th Wheel Trailer
    It depends on how you want to connect the batteries; in series or in parallel. Batteries that are wired in series will double the output voltage and keeps capacity the same. So for example if you are using 2 identical 12 volt batteries connected in series the output voltage would be 24 volts and the amp hour rating would be whatever it says on one of the batteries. If the same 2 batteries were connected in parallel they would be putting out 12 volts but the capacity would be doubled. I...
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  • Why is My Trailer Wired with 24 Volt Electricity
    The main reason that trailer manufacturers use a 24 volt system over a 12 volt system is because of the reduced wiring cost. Increasing the voltage of a system will cause a reduction in current which in turn reduces the size or gauge of wire needed. The other benefit is its compatibility with AC current more so than that of a 12 volt system.
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  • Where to Run Black Wire of 37185 Adapter on 2017 Toyota Highlander Hybrid
    You did everything correctly. The black wire of the # 37185 would need to go to the terminal that attaches directly to the positve post like you did. The other post looks to be circuit protected and for a different accessory so bypassing that would be the correct method.
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  • Are Trailer Brakes a Requirement
    A brake controller is only required for electric brakes or electric over hydraulic brakes; however, trailer brakes themselves may be needed depending on the weight of your trailer and your local laws so you will need to check with your local transportation office. Additionally you will want to check the owner's manual of your Jeep Grand Cherokee as it may say trailer brakes are either needed or recommended for trailers of a certain weight. If your trailer does need brakes or you need...
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  • Would Install of Brake Controller in Truck Cause Damage to Transmission Potentially
    A brake controller would have no affect at all on the transmission of a truck. We've heard of some pretty strange things said by confused mechanics but this is incredibly strange... A brake controller only helps the vehicle and trailer stop when towing. This prolongs the life of the brakes of the vehicle and also makes towing substantially safer. Removing a brake controller for fear of transmission damage is one of the dumbest things I've heard to be completely honest. If a brake controller...
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  • Recommendation for Connecting 4-Way Flat to 7-Way Connector on Trailer
    It sounds like you are just needing the Hopkins Adapter 4-Pole to 7-Pole and 4-Pole # 37185. This will plug right into the 4-Way flat on your tow vehicle and provide a 7-Way to connect with your trailer. Since you are only needing to power the lights on the trailer, the additional wires can simply be tied off as they will not be needed. I have attached a short video demonstration on this product that you can also check out.
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  • 4-Way to 7-Way Adapter for Truck Towing Trailer with 7-Way
    Sounds like what you need is the part # 37185. This adapter will allow your truck 4-way to plug in and provide you with a 7-way for the trailer to connect to.
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  • Which Pins of 7-Way Round and Blade Carry Brake Output
    Running the brake output circuit from your round 7-way to the blade style 7-way would be what you would need to do. On the blade 7-way the brake circuit is the 5:00 pin and on a round 7-way it's typically the center pin. The breakaway kit would be on the trailer so you'd need to check it out to be sure it has that. I would be surprised if it didn't. That's not something you can install on the tow vehicle. I attached a help article with more info on breakaway systems as well.
    view full answer...
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