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.
This circuit tester plugs into the four-way trailer connector on the vehicle. The bright LED lights analyze the trailer connections and indicate which functions (tail, left turn and stop, right turn and stop) are working properly and which are not.
Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.
Hey everybody, Ryan here at etrailer. Today, we're going to be taking a look at the Curt four-pole vehicle side trailer, wiring tester. So, if you guys have ever towed a trailer before I'm sure you have encountered this problem. You get all hooked up, and kind of do a walk around, you know you kind of do a pre-trip before you hit the road. You check a few things out, one of them being the lights. And, of course, you turn your blinkers on.
Maybe you have a light out at the trailer. You hit the brakes or the tail lights and something's wrong. And then this kind of turns into a headache. You know, you're, you're checking your vehicle side, checking fuses, making sure everything's good there. Then, you get the going on the trailer side.
It's kind of just a big mess. And one thing you can do to isolate that problem is use a vehicle side tester like this. So, the way this is going to work, is it's going to plug into your vehicles four way flat connector. All right, and then that's going to isolate the problem. So, once you plug this in, you can run through all of your signals and your lighting functions.
And if they all work back here, then you know, okay something's going on with my trailer and you can focus your time on that. If you don't have all your functions back here chances are good. You could say, okay, trailer's probably okay. I probably have an issue with my vehicle side and you can focus your energy there. So, at the end of the day, if you do have an issue, it's a great little tool that can potentially save you a ton of energy.
So, whenever you are plugged in to your vehicle side, you can test the function. So we're going to have our left turn signal, our right turn signal, our taillights, and our brakes. So, since these lights are LEDs, really easy to see, even on a sunny day like today, which is convenient, especially if you're by yourself, kind of trying to, you know if you have miring stored inside you can hold it up or mount it up and check it while you're in the driver's seat, so you ain't got to get out of the car every time. But, since we don't have any labels or anything here, I figured it'd be useful to share what lighting function illuminates the light on the test, or if that makes sense. So, this light here should turn on when you use your right turn signal, the one next to it should turn on when you use your left turn signal, both of these lights should illuminate when you apply the brakes, and this one should come on whenever you have on your tail lights. So, let's say if you're, you know, testing your, your right turn signal, this one should be flashing. See, this one isn't, but this one is, okay So, you're still getting something to happen, but on the wrong circuit. So, that could help kind of direct you as well to get it figured out. You may have a short or something like that in the electrical system, and that could be looked at. So, when it comes to this tester, honestly, this is probably the last one you'll ever need, unless you lose it or something like that. Things are actually pretty, pretty stout. They're pretty solid. These are actually the exact ones we use here at the shop. And we use them day in and day out, all the time, and we've had them for years. They still work like they should every day and they really take a beating, and they just continue to work. So, for the average person to use them, occasionally, I mean this should last for the life of your vehicle or the life of your trailer, and then some. So, really nice, you know, it does have a key ring holder on the top there. And what we do, here at the shop, is usually put a zip tie or some type of key chain on there just to make a little larger so we can hang it up. If I had, you know, if I was going to keep one in my personal vehicle, something like that, you know, I'd probably end up using a key chain with my trailer lock and everything else on it, throw it in the glove box, so you always have it. So, it's a little nice touch and something I thought was worth mentioning. So, as I mentioned, this could work for your four way flat type connectors and it just plugs right in, just how you'd plug into the trailer side. And if you have multiple vehicles or different trailers, things like that and you need a different type of tester, not a big deal. We offer other ones as well. Whether you have a five way or a round seven-pole something like that. There's going to be a tester similar to this available here. That way you can use it for that wiring as well. And that'll finish up our look at of the Curt four way flat trailer, wiring tester..
Customer Satisfaction Score:
99% were satisfied with this product
1% of customers were not satisfied
Ratings & Reviews
great price, fast shipping, tester works great, the Curt 4 way flat tester helped to determine that the problem was with the trailer and not the vehicle
It works, it seems to be put together well and should last pretty close to forever. There were no instructions, so I couldn't tell if the left and right might be crossed in my vehicle wiring. However, I got a fast response to my question and the bottom of the product page now shows which light is which. All in all, outstanding - good price, fast shipping, and quick response to my question.
Sherwin
7/3/2014
Great! No problems.
Works as advertised! I'm glad I got it because it makes life just a little bit easier
After wiring up the harness this tester shows various lights when brakes, running lights and turn signals are activated. The only problem is that the lights are not labeled so you don't know what light circuit is being activated. With the harness I wired there was no way to wire it wrong ( just plug n play) so it should be correct.
Have to wait until trailer is attached to be sure.
Mike L.
4/6/2019
The tester has one socket and three pins. The pin closest to the socket is the Running Lamp circuit, next is the Left TurnBrake Lamp circuit and last is the Right TurnBrake Lamp circuit.
Order has been received.
Installation was completed 3 days later.
The installation video was most helpful on your site.
The followup on the order has also been impressive.
The unit is now in service and operating as described.
This item cost significantly more than an "off the shelf" harness but the extras such as the overload protection module and custom connectors seemed to add value. In fact, I am very pleased thie the unit, process and ease of installation. I would do this again without hesitation and would recommend your site to anyone.
The time and frustration usually dealt with in performing this type of installation in the past make this a very worthwhile investment.
Issues I did experience:
The tracking of the item from shipment and through 3 handling centers in the U.S. took 4 days
The handling of the package once in Canada, through 3 centers took 9. This delay over the border meant that I missed my first opportunity to utilize the vehicle on its' first assignment. Unfortunate but not really a reflection on etrailer.
The mounting bracket ordered did not fit on the trailer hitch I received, which was a round main support with no flat surface for the mount bracket. Once I was able to create a mount location, the next challenge was the extreme pressure needed to seat the electrical socket into the bracket. Eventually this was accomplished. Upon first use, the socket easily slipped back out of the bracket. Reversing the bracket, the result was the same, difficult to insert, easy to push back out. I have made other arrangements without the mounting bracket.
Overall, I am pleased with the result and would do it all again.
Thank you and etrailer for the follow up and the product.
The LAST time we fiddled with our old vehicle and hitch, we nearly ripped out our hair, trying to figure out why the lights weren't working before we figured out the mice had eaten a wire inside the truck. THIS time around we picked up this handy little gadget which tells you if it's working and, as a bonus, plugs out the loose ends so they don't get all corroded.
Anna
5/20/2019
We are very happy with our trailer hitch, and all the accoutrements that we purchased with it. Your videos were enormously helpful, the hitch went on easily with a bit of help from our teenage daughter to lift it up into place, and we recommend your business to friends when they express an interest in getting a camper.
Works well, all lighting tested positive
Just what I needed to be sure trailer lights are wired properly. I'm in Florida now, trailer is in Ohio. Put hitch and wiring harness on new 2020 SUV, but won't be back to Ohio for a couple weeks. Nice to know that everything is ready while I have car dismantled. Low price, fast delivery. Thanks
Craig
5/16/2021
Perfect. Easy access, plugs right in,has rubber cap to keep weather out of plugs.
This little connector is a lifesaver for a first-timer installer of the 4-pin trailer harness. You need to have the ignition on for this connector to work, you don't have to have your car turned on though. It looks very well built and I like the fact that the LED lights are covered and protected. Not much to do with it once you've tested your trailer harness, but it's one of those tools that it's best to have than not.
Ricardo Z.
8/17/2021
Well, I havent used it since that first time. This product to me is a one-time use. But I still have it and have no plans of reselling it or whatever, I dont know when Im going to need it again so its best to just keep it in a safe place.
I purchased a Curt Trailer hitch for my 2013 Toyota Tacoma. While shopping on your site I noticed this handy gadget for testing the wiring harness. Although I have not yet installed the hitch or wiring harness, I am certain that this tester will be extremely handy for testing the wiring. I am also very impressed with the videos that you have produced showing the installation of the products that you sell. I am sure that the installation of these items on my truck will be accomplished without a "hitch".
Thomas
8/26/2019
Product is working great! I will be turning to etrailer for all of my towing needs.
Once I deciphered how to interpret the lights, I was extremely pleased with the Tester. Your installation video for my wiring harness was where I learned how to interpret the lights, as there are no instructions included with the tester.
I had placed an order from etrailer for a trailer wiring kit, as I'm going to be renting a uhaul trailer to move some stuff. The wiring kit looked fairly easy to install (based on a video on etrailer), but it then occurred to me that I wouldn't know if I installed it correctly until I picked up the rental trailer, and then it would be too late to do anything about it. So I looked at various testing tools and this looked like the easiest (and cheapest).
It worked exactly as promised. (Turned out I installed the wiring kit correctly.)
My only suggestion is that there should be a tag (or label, etc) on the tester indicating what light should light up for what function. I know the etrailer website shows which light is for which function (ie brakes, lights, turn signals), but it would make sense to enclose this info with the device.
That said, this was easy to use and did exactly what it should.
Bjb
7/20/2015
The wiring kit I bought continues to work just fine. Im also glad to have purchased the small wiring tester at the time - the first time I rented a trailer the lights werent working without the tester, I would have assumed the problem had to do with the installation of the new wiring, but this gave me the confidence to know the problem was with the rented trailer and I could insist they come and fix it which they did.Anyway, still very pleased with the purchase, and would continue to recommend it.
It is always a pleasure doing a project that I source through etrailer.com. I bought the draw-tire hitch, wiring harness, and a couple of other things I needed for the install. Everything ordered was packed in a single shipment. It arrived earlier than expected and undamaged thanks to the care they take in packing the items.
It all went into the car as described in their videos. I love the videos they produce and post to their site. They are such a help in both shopping and execution of the project. Thanks guys!
Here’s a pic of the completed installation.
Works great. A handy product to make sure all lights are working.
It came in handy to help my neighbor troubleshoot his new trailer wiring
This was a great way to check to make sure the electrical connections are all right. Very simple
it worked. makes pinpointing problem ea sier
This worked great. Along with the expert advice on my question, all the trailer lights are functioning perfectly. Thank etrailer
Great price, quality and delivery. This tester worked great to let me know that everything was hooked up and working correctly.
Made well. Made confirming harness installation was working correctly prior to hooking up to a trailer (which could be bad and therefore create a troubleshooting project). Lesson Learned: Make sure the connector is mounted such that the tester lights are facing rearward. I had to remove and re-install the connector which was not easy.
Handy little tool to have on hand to verify your wiring. Quick and painless testing for wiring up a 4 pin connector. Did require a 2nd pair of hands to hold it up while I tested all the lights and functions.
James
5/16/2025
This little tool works great. Ive used it a few times to make sure everything was working and troubleshooting a blown tail light on my trailer. Handy little tool to have in the glove box if youre towing.
This tiny unit is very helpful for verifying that all the wiring works after installing your wiring harness. You just plug the unit into the end of the vehicle's trailer plug. This will also be helpful for troubleshooting vehicle vs trailer wiring issues.
Works great for testing your lights on your vehicle before hooking up your trailer.
Wayne
10/9/2025
Still working great, I highly recommend it.
Tester worked fine, showed I didn’t have running light, got replacement harness from trailer, still no running lights. Phone call to tech service not helpful, call to BMW won’t discuss it, so I have a trailer W/O running lights.
On your video they had
Bruce N.
11/13/2025
Not the best, still no running lights , no ne seems to be able to solve the issue. I tried a second unit and still had no running lights
Item worked well but having no markings on what each light meant and no instructions was annoying. After looking online I was able to find a drawing of what each light meant.
Also when standing behind your vehicle with the tester plugged in be sure to have led lights on the tester facing down towards the ground to get correct reading.
Do you have a question about this Electrical Tool?
Info for this part was:
At etrailer 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.
Mike S.
1/15/2018
i havent really had a need to use the tester since my first use. it was very helpful in locating the problem i was having. i have since corrected the problem and havent had any other issues since then. the tester is in my tool box should i need it again in the future. thansk for checking back, hope you have a great weekend.