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Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover - 7-Pole to 4-Pole or 5-Pole

Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover - 7-Pole to 4-Pole or 5-Pole

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Reese 4 Flat,5 Flat Trailer Wiring - 78118
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This adapter lets you quickly convert your 7-way connector for use with a 4-way or 5-way flat trailer-end plug. It includes a circuit tester with red LEDs and a built-in dust cover that protects the terminals when you aren't towing. Great Prices for the best trailer wiring from Reese. Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover - 7-Pole to 4-Pole or 5-Pole part number 78118 can be ordered online at or call 1-800-940-8924 for expert service.
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Reese Trailer Wiring

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This adapter lets you quickly convert your 7-way connector for use with a 4-way or 5-way flat trailer-end plug. It includes a circuit tester with red LEDs and a built-in dust cover that protects the terminals when you aren't towing.


  • Easy-to-use, plastic adapter converts your vehicle's 7-blade, RV-style, vehicle-end connector for use with a 4-wire or 5-wire flat, trailer-end connector
  • Circuit tester with highly visible, red LEDs
    • Lets you check the connectivity of your electrical circuits at a glance
  • Built-in cover protects terminals from dust and grime when you're not towing a trailer
    • If you use dielectric grease, the cover keeps the plug clean for storage
  • 1-Year limited warranty

78118 Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover - 7-Blade to 4-Pole or 5-Pole

Item # 78118

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Video of Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover - 7-Pole to 4-Pole or 5-Pole

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

Video Transcript for Reese Trailer Connector Adapter with LED Circuit Tester Review

Hey guys, it's Randy here at Now a common question that we get here is how do I adapt my seven pole on my vehicle to work with a trailer that has maybe a different connector on it As you can see here we're going to take a look at the Reese Towpower adapter. Now this adapter is going to take care of a lot of different things for it. I really liked the way this deal works. Basically this is going to plug into your seven pole. It's going to give us a working five pole, a working four pole, but also if you can see those little red LEDs in there.

This is going to diagnose a trailer connection problem that we might have. So with this plugged into our vehicle, we'll turn on our headlights, make sure that the tail light bulb comes on, left blinker, verify that. Right blinker, verify that.Then hit her brakes and make sure they both come on. This is going to ensure that we don't have any problems with our vehicle, so we're going to know from that point the issue we're looking for is in our trailer. It eliminates half the equation just by plugging it in.

I think that is really neat. Now where this one differs from a lot of the other seven to four and five adapters that we offered, that his one actually has a four pole slot and the five pole slot. The five pole slot is going to give us our ground running lights, our left turn and brake, our right turn and brake, and our reverse signal.Now that fifth pole is for our reverse signal. We're going to use that reverse signal most of the time in a marine trailer application that has an electric lockout for its surge brake. As you back up, you put pressure on that.

That can apply the brakes in the trailer. It's kind of a situation if you can't back your trailer up. So by sending that circuit to that lockout, that fluid isn't transferred, we can easily back up. A lot of customers also ask if you can run backup lights on your trailer off of that circuit, and you absolutely can mount a couple of lights back there. When you hit reverse they're going to come on.

They'll illuminate the ground behind you.Now on the four pole side it's going to have all of those same signals with the exception of the reverse. Now most adapters like this are just going to have the five pole, your left to stick the four pole in. The reason I like this being this way, with the shrouded four pole connector it's going to have a black shroud that goes all the way around here where these are kind of down inside it comes up to about here. If you're trying to connect that onto a five pole, that shroud gets in the way right there and it won't allow you to connect it properly. So this completely eliminates that issue. Any four pole, it's going to sit right in there. You'll see the accommodation going around the outside here for that sleeve to fit into. I think they really thought this out really well to ensure that we're going to have good long lasting life out of this for one, but also that it's going to work in the application where we need it.You can also see it's got a dust cover here. We don't see that on all the other ones that are out there. That's going to sit down and over whichever one we're not using. So if we're using our four pole side, we'll cover our five pole side. If we're using our five pole side, we can cover our four pole side, so this is gonna work out in all weather conditions. You'll see that in the reviews. Customer say regardless of the weather, regardless of the situation, this thing works out really well. The installation's going to be just like a regular seven pole. Lifting up our cover here you can see the tab on top. That needs to go behind the tab on our door, place it in. Wiggle that into place. Let that come down and capture it. Then it's just a matter of getting our four pole plugged in there. At that point, just check our lights really quickly, but you'll be ready to head down the road knowing that you've got the signals you need heading out where you need them.Now, let's take a quick look at the diagnostic function and see if we can turn on those headlights. It's going to show us that those are in fact coming on. And we can check our left blinker, our right blinker, and our brakes. That's going to help us ensure that everything on our truck sides working, so we should look at our trailer if we're having any problems. Now there's several other options out there as far as adapters go. I really like the way this one's built. They put a lot of thought into it and I like that it has the tester included. In other situations if you need something with an extension, those are out there and available to give you a little bit more of links on your plug. But all in all, I think it's a really nicely made product. It seems like they put a lot of consideration into how it's going to be used and it's one I would definitely own if I had the need.

Customer Satisfaction Score:

Customer Reviews

Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover - 7-Pole to 4-Pole or 5-Pole - 78118

Average Customer Rating:  4.9 out of 5 stars   (72 Customer Reviews)

This adapter lets you quickly convert your 7-way connector for use with a 4-way or 5-way flat trailer-end plug. It includes a circuit tester with red LEDs and a built-in dust cover that protects the terminals when you aren't towing.


Use it to check my motorhome 7 pole operation and plan to use the 4 pole connector for my curt auxillary LED light that I will attach to my bike rack when its on the motorhome and SUV. Recently used the 4 pole to power car dolly light system on a 900 mile trip. No issues.



Still works. Rarely used in the past year.


A great product


Worked just as described. Very convenient plug. All good.


My first experience with etrailer. It was a pleasure. Great products at reasonable prices, with fast shipping.
This adapter performs as advertised. It is a very convenient way to test your vehicles wiring, without having your trailer hooked up.
If I were to be really picky, I would have liked it to have a tighter fit in the vehicle's socket. I'm sure it will be fine though.
I would definitely recommend etrailer!


Works great for the basic checking of turn, brake and running lights. Overall fit and design is great.



Excellent adapter makes checking the harness easy.


Superior unit. Great idea having the diagnostic LEDs. Suggest adding a case or draw string bag for storage when not in use.


I received my trailer wiring harness today and I was so impressed! The details and video of what I was ordering, made the process easy. Even though it said when I would receive it, I figured that during this Christmas time, it would take longer than projected. It came on time!
Thank you!!
Augusta Georgia


Just what I needed for the two trailers I have, one with 4 pins and one with 5. Nice dust cover for the one not in use as well.


I find this product very useful when determining where my trailer light problems are. Having the LEDs built into the plug is a great idea.


Item worked as stated fit good and stayed in place. shipping is fast and easy, item came a day early. Etrailer has great pricing an a great selection.

Frank D.


Product works as it did on day 1. Holds up in all types of weather. Hats off to Etrailer for a product that works as advertised


Fits perfectly and seems to work although I haven’t actually hooked the trailer wiring to it yet. But the leds light as expected.


Product works as advertised. LED lights work great to check for faults in trailer or vehicle circuits.


Seems well made. Needed for my 2015 Chevy Surburban since it only has 7 way plug and I needed 4 way also. The test lights should come in handy in the future.


Seems to be as advertised. The dust cover is only on the 5 pole connector.


Great adapter with the tattle tale LEDs to indicate what lights are energized for trouble shooting circuit problems.


Works great


Exactly what we needed for our new 2020 Honda Pilot with the towing package. Shipment was prompt too!


Does the trick, converts my 7 Pin to 5 pin.


Great product , well designed for my boy trailer , 25 Foot Rosborough .


Well built outstanding adapter. Indicator lights make quick check of lighting systems.


Every time I purchase something from ETrailer it makes me grateful I found this company. Quality product, fair prices, fantastic customer service.
Thank You Odelia!


Awesome product


Received it very quickly. Still need to try it on my boat hitch that is in storage! Praying it works!


Shipped and received FAST! Exactly what I was looking for.


Works great, good value, looks like it will hold up well

Mike M.


Working as it should

Show More Reviews

See what our Experts say about this Reese Trailer Wiring

  • Which Pin on Reese 78118 Trailer Connector Adapter Goes Hot With Vehicle In Reverse
    On your 7-way on the vehicle, the center pin would power up when the vehicle is put in reverse, assuming that the 7-way was correctly installed. On the # 78118 adapter, the pin all the way to the right will power up when the vehicle is shifted into reverse. I've linked a demonstration video for the # 78118 Adapter.
    view full answer...
  • Troubleshooting 2 Lights Blinking on the Reese Trailer Connector Adapter # 78118
    The only reason two of the lights would be blinking under normal circumstances would be if the circuits that were blinking where the left and right stop/turn signals and it was because you had the emergency flashers of your vehicle on. Otherwise that indicates you have some kind of short and I would recommend you check the back of your vehicle connector for corrosion or any other obvious problem such as exposed wire and fix as necessary.
    view full answer...
  • How do the LED Lights Work on Reese Trailer Connector Adapter w/ LED Circuit Tester 78118
    The LED lights on the Reese trailer connector adapter # 78118 will tell you if the corresponding circuit is working. The light on the far left will tell you if the running light circuit has power. There is a T next to it for Tail Lights. In the middle is the light for the left turn/brake light circuit. And the far right is for right turn/brake lights. If you turn on the vehicle head lights then the T light will be on. If you step on the brakes, the other two will light up. Or if you use...
    view full answer...
  • Can the 4-Way and 5-Way of the Reese Trailer Connector Adapter # 78118 be Used at Same Time
    Yes, both the 5-way and the 4-ways of the Reese Trailer Connector Adapter # 78118 could be used at the same time. Since a 4-way can plug into the 5-way you could use both of your 4-way connectors. You would need to also be sure not to overdraw the taillight circuits of the vehicle's wiring. Powering two sets of trailer lights may be too much for the adapter.
    view full answer...
  • Running Lights Not Working With Reese Trailer Connector Adapter w/ LED Circuit Tester # 78118
    Since you mention that the LED light on the Reese Trailer Connector Adapter, # 78118, isn't illuminating for the tail lights, it sounds like the issue is with the truck but this could be something as simple as dirt or corrosion in the 2013 Ford F-150's 7-way connector. If the pin looks clean then the issue may very likely be a blown fuse or faulty relay. If everything checks out to be fine and the running lights on your trailer still aren't functioning properly, please feel free to email...
    view full answer...
  • Will Reese 78118 7-Way to 5-Way Adapter Work Well Towing Boat Trailer with 5-Way
    Yes, the Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover # 78118 that you referenced would be exactly what you'd want. This will plug into the 7-way of your Tundra and give you a functional 5-way to use with your trailer that has surge brakes. In case you were curious the 5th pin of a 5-way carries the reverse light circuit which is what activates the reverse lock out solenoid on your trailer that will allow it to back up without applying the brakes.
    view full answer...
  • Can LED Lights on Reese Trailer Connected Adapter Drain Vehicle Battery
    The Reese Trailer Connector Adapter # 78118 will not drain your vehicle battery. The power draw from the LED lights is next to nothing so it isn't a concern. In fact, that may be why the lights are staying on. If there is lingering power after you turn off the vehicle it could keep the lights illuminated for quite a while. Try checking a few hours later to see if they are still on. Even if they are, again, it won't be pulling enough power to drain your battery. If it makes you feel better...
    view full answer...
  • Availability of 7-Way to 4-Way Adapter that Fits 2003 Toyota 4Runner
    Yes, the 7-way adapter part # 37385 and # 78118 will both fit the factory 7-way you have on your 2003 Toyota 4Runner. They will simply plug into the 7-way on your vehicle and be ready to go.
    view full answer...
  • Circuit Tester for 7-Way Trailer Connector that Includes All Circuits
    The 7-way circuit tester part # 6562 tests all of the 7-way circuits including the two you mentioned of brake output and 12 volt accessory. I attached a review video for this for you to check out as well.
    view full answer...
  • 2013 Jeep Grand Cherokee 7-Way Not Showing Turn Signals or Brake Lights
    If you're not getting turn signals or brake lights on the vehicle, it is possible there is a blown fuse in the fuse panel. Your owners manual has a diagram with the fuse panel and can help you determine the correct fuse to pull and replaces. I have attached Reese # 78118 to help you test your 7-way on the vehicle. If your wiring issue is on the trailer, follow the wires from the plug on the trailer to the tail lights and look for any spots where the wire insulation has been frayed or look...
    view full answer...
  • Comparing Reese and Hopkins 7-Way to 5-Way Adapters
    I'd recommend the Reese # 78118 7-way to 5-way adapter over the Hopkins part # HM47675 that you also mentioned because the Reese comes with a circuit tester which for most people would be more useful than what the Hopkins has instead which is a 12 volt power circuit. There are quite a bit more situations where people are in need of a circuit tester than a 12 volt power supply so I believe it would be much more useful to you. I attached a review video for the Reese for you to check out as well.
    view full answer...
  • Will Tow Ready TR20141 Work on Foreign Vehicles Only
    According to my contact at Tow Ready, they have heard of the issue you describe and have received comments from customers experiencing the same problem who used a standard # 78118 adapter which worked fine. They haven't tested the # TR20141 so they didn't have any input on that. The # TR20141 will work on any vehicle that has bulb-out sensors which are featured on many European vehicles. The adapter uses an inline resistor that draws a bit more power which fools the bulb-out sensor.
    view full answer...
  • Only Left Trailer Light Shows Power with 1999 Chevy Tahoe
    There are several things you can check to determine why a trailer wiring circuit is not working. First, you will want to test the vehicle side trailer connector using a circuit tester such as #PTW2993. Have someone sit in the vehicle and go through the light functions while testing. If everything works on the vehicle you can move on. If a circuit is not working on the vehicle, then make sure the trailer connector is clean and free of corrosion inside and out and inspect the wiring, fuses,...
    view full answer...
  • Adapter for 4-Flat on Truck and 7-Way on Trailer
    We do have a solution for you, though the Reese Trailer Connector Adapter # 78118 will not work for you. Instead I recommend the Hopkins Endurance Quick-Install Trailer Connector Adapter # HM47200 which will plug into your truck's 4-way and allow you to connect your trailer's 7-way.
    view full answer...
  • Recommended 7-Way To Use With the Reese Towpower LED Lighted Hitch Step 7065300
    The best 7-way trailer connector to use the Reese Towpower LED Lighted Hitch Step 7065300 is going to be largely dependent on the year, make, and model of the tow vehicle. However, the 7-Pole and 4-Pole Trailer Connector Sockets part # HM40975-11998 is what I recommend using as it has both 4 and 7-way trailer connection points, comes with a mounting bracket, and has a removable wiring harness pigtail which is easy to install using the included connectors.
    view full answer...
  • Looking for Adapter to Convert 7-Way on Vehicle to 5-Pole Connector on Trailer
    I'm assuming you're needing the adapter for a boat trailer that has a surge or hydraulic coupler. The 'brake' wire doesn't carry power to the trailer brakes, it merely 'locks out' the hydraulic coupler when the vehicle transmission is shifted into reverse so the trailer can be backed up without the trailer brakes coming on. If this is the case, I'd recommend the Reese # 78118 adapter, that's compatible with either 4-pole or 5-pole trailer connectors.
    view full answer...
  • Best 7-Way To 5-Way Trailer Adapter For a 2019 Ram 1500 Pulling Boat Trailer With Electric Lockout
    I recommend the Reese Trailer Connector Adapter w/ LED Circuit Tester and Dust Cover # 78118. This is one of the only adapters for your 7-way to 5-way that has the led test lights. This will help you troubleshoot issues that you may have with the trailer lights.
    view full answer...
  • Adapter Kit to Allow Trailer Wiring of 2021 Mercedes Benz Sprinter to Activate LED Lights
    For a 7-way adapter designed for German vehicles towing LED lighted trailer to prevent the bulb out error message we have the part # C57003. For an adapter that plugs into a 7-way and then provides a 4-way we have the part # TR20141. Since it sounds like your LED kit uses a 4-way the kit you'd want is the # TR20141.
    view full answer...
  • Adapting a Semi Truck 7-Way to RV Style 7-Way to Use Wireless Light Kit to Flat Tow a Van
    There isn't an adapter to go from a semi-truck 7-Way to an RV style 7-Way, but you could hardwire in a separate RV style 7-Way on the semi-truck. You can use a circuit tester such as # PTW2993 to test the wires at the back of the semi 7-Way. It should have separate circuits for each turn signal and brake lights. If so, then you will need to combine the separate circuits using a converter # RM-732 because an RV style 7-Way has combined turn signal/brake light circuits. On the converter...
    view full answer...
  • Do you Have An Installation Video For the Draw-Tite Trailer Hitch Receiver on a 2018 Ford F-150
    I have included a link below for an installation video for the Draw-Tite Max-Frame Trailer Hitch Receiver # 76136 that we installed on a 2018 Ford F-150. Also is a video for the Curt T-Connector Vehicle Wiring Harness # C56413. This will give you a 7-way connector for plugging in your trailer. The Reese Trailer Connector Adapter # 78118 will allow you to plug into a 4-way or 5-way flat trailer if you are pulling a small trailer.
    view full answer...
  • Recommended Trailer Hitch Receiver and 7-Way Wiring Harness For a 2023 Chevrolet Traverse
    I recommend using the Draw-Tite Max-Frame Trailer Hitch Receiver # 76184 on your 2023 Chevrolet Traverse. This receiver is designed to install behind your rear fascia and is accessible by the removable panel on the rear fascia. It has a welded tab which will allow you to install a Mounting Bracket # PK12711U to attach a 7-way connector. The T-One Vehicle Wiring Harness # 118287 will allow you to add a 7-way connector to your Traverse. An Adapter # 78118 can be used when towing smaller...
    view full answer...
  • Trailer Hitch Receiver and Wiring Harness For a 2020 Ram ProMaster 1500 Cargo Van
    Yes, the Curt Trailer Hitch Receiver # C13295 is confirmed to fit your 2020 Ram ProMaster 1500. I recommend installing either the Tekonsha 4-Way # 118618 or 7-Way # 22112 depending on your needs for the type of trailer you will need to tow. The 4-way is primarily used for small single axle utility trailers, while the 7-way is mostly used on larger trailers that use electric trailer brakes. If you for see using both connectors the 7-way will allow you to use an Adapter # 78118 to go down...
    view full answer...
  • Vehicle Wiring Harness For a 2018 Ford F-150 That Did Not Come With a Factory 7-Way
    The Curt T-Connector Vehicle Wiring Harness # C56413 will connect to the factory wiring below the bed on your 2018 Ford F-150. This will give you a 7-way connector that you can mount below your bumper with the Curt Mounting Bracket # C67UR. You can then use a Reese Trailer Connector Adapter # 78118 if you will be towing a smaller trailer that only requires a 4-way connector. Or you can change out the connector and bracket for the 7- and 4-Pole Trailer Connector Socket w/ Mounting Bracket...
    view full answer...
  • Comparing Tekonsha Universal 7-Way Versus ETBC7L Install on a 2023 Kia Telluride
    Using the Universal Wiring Harness w/ ModuLite and Brake Controller Harness # 22551 on your 2023 Kia Telluride will allow you to use a dash mounted brake controller like the Tekonsha Prodigy P3 # 90195. It also only has a 7-way connection which would require you to use an Adapter # 78118 for a smaller trailer with only a 4-way connectorl The combination of the Curt Powered Tail Light Converter # C59236 and 7-Way RV Upgrade Kit # ETBC7L would require you to use a wireless/Bluetooth brake...
    view full answer...

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