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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
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
Wayne
10/9/2025
Still working great, I highly recommend it.
Nick S.
10/9/2025
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.
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.
Thomas
8/26/2019
Product is working great! I will be turning to etrailer for all of my towing needs.
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.
Craig
5/16/2021
Perfect. Easy access, plugs right in,has rubber cap to keep weather out of plugs.
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.
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.
Sherwin
7/3/2014
Great! No problems.
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.
Dan M.
5/26/2021
Excellent
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Harold
9/10/2026
Had been an extra tool for checking lights, all works out.