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Hooking up trailer lights can be a hassle when you have to splice into factory wiring. This Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector skips all that. It plugs right into the existing tail light wiring to give you a working 4-flat connection. No cutting or splicing—just plug it in and it’s ready to go.
Once installed, the 4-flat connector provides the standard functions—running lights, turn signals, and brake lights—for most small and mid-size trailers. It’s a simple, proven setup that keeps your trailer visible and legal on the road.
Because it’s a hidden, plug-in style harness, the wiring stays tucked away and out of view when you’re not towing. That means no loose cables hanging off the back and no need to modify body panels or trim pieces during install.
The included red wire makes this harness flexible for different vehicle lighting systems. If your vehicle uses a 2-wire system where the brake and turn signals share the same light, ground the red wire. If it uses a 3-wire setup with separate brake and turn lights, just leave that wire intact. It’s built to adapt cleanly either way.

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.
Hi there. I'm Michael with etrailer.com. Today, we're gonna take a quick look at this Curt t-connector custom vehicle wiring harness. Now this harness is going to provide a four way flat trailer connector at the back of your vehicle so you can hook up to and power your trailer's signal lights. This setup is going to be very easy to get installed because it is a custom fit for your 2021 and newer Hyundai Elantra. So this will have these plugin play connectors that are going to make it very simple to get wired in place.
You're not gonna have to worry about cutting your vehicles, wiring, splicing in, anything that could damage your vehicle's original wiring. This is gonna be a very simple solution for you. This kit is going to be compatible with five pole, six pole and seven pole adapters. So if your trailer has a five pole, six pole or seven pole instead of the four way flat, we do have adapters available for you that will convert that so that you can still use your vehicle's signal lights and send that back to your trailer. They also include a dust cap here to protect your connections.
It fits right in over top of your floor pole plug there. And then you can cover up those connections make sure that no dirt, debris, moisture and that sort of thing can get to those connections. Like I said, this is going to plug right into your vehicle. So very simple to do. They do include very detailed instructions to walk you through that process, but just a very, very quick overview.
You will need to get access behind your vehicle's tail lights. That's where you'll find plugs that look very similar to this. That's connecting your taillights to your vehicle wiring. You'll just separate those plugs and put this in line, connect them to the matching connectors. And then that's going to recomplete that circuit so your tail lights will work like normal whether you're hooked up to a trailer or not.
But then it will also send that signal down to your plug so that you can send that back to your trailer. So your red, brown and yellow is gonna be on your driver's side. You'll do the same process on your passenger side. You'll just route this green wire over to those passenger side tail lights and plug those in there. They do include a rain terminal for your ground as well as a self-tapping screw. So you'll just ground this to metal back there around that same area. You'll want to run your wiring to where it's gonna be convenient to hook up to your trailer somewhere back towards the back of your vehicle. And then you're gonna have this black wire that's going to run up to your battery compartments. That's probably gonna be the most difficult part of this installation is running this wire. So they do include some butt connectors there. So you can connect this black wire to this extra wire that they have and route this up to your battery compartment. You do wanna make sure while you're routing this that you're staying away from anything that's hot or moving that could potentially damage the wire. They do include some zip ties here so that you can keep it up out of the way, off the ground so you don't have to worry about it dragging. Once you get up to the engine compartment, you'll then take the other end of that wire, connect it to your fuse holder here. The other end of your fuse holder, we'll connect it to your ring terminal. Connect that on. Put that onto your positive battery post on your battery. Once everything's hooked up properly, then you can put your fuse in there and that will then send power to the unit. So this is going to be a tail light converter. That's going to ensure that your vehicle's wiring matches that of your trailer. It's also going to be powered from your vehicle's battery. So it's not gonna be pulling or draining your vehicle's electrical system. That's currently sending power to your lights. So rather than potentially overloading that system, it's gonna draw power from your battery so everything's gonna work properly and no worries about overloading that system. And this unit will mount back in that same tail light area. They do include some double sided tape here that you can just peel off the back and set that in and then find a good area to mount this to. So, straightforward installation. Plug and play for this portion. Really the most difficult portion will be running that wire up to your battery, which is still definitely doable. It's something you can do on your own in your garage over the few hours on the weekend. Something along those lines. Definitely don't need to pay a mechanic to do it for you. So this is going to provide three amps per circuit for your stop and turn lights and six amps per circuit for your tail lights. I think if you're wanting to pull a trailer you're wanting to make sure that you have those lights operational. This is gonna be a great system for you. I installed a system very similar to this on my wife's vehicle. I didn't take very long at all. I think it's definitely something that just about anybody can do. That completes our look for today. Again, I'm Michael with etrailer.com. Thanks for watching..
Customer Satisfaction Score:
82% were satisfied with this product
18% of customers were not satisfied
Ratings & Reviews
Very prompt delivery. Excellent packaging. Excellent service! Would have given 5 stars but the hitch was pretty roughed up and paint scuffed off in several places. Certainly had to happen pre-packaging. I will keep and touch up before installing.
Shipping was fast. Received item with a previously opened hard plastic wrapper, with packing tape applied. Most sellers admit to open box items and give a discounted price, not so in this case! All parts seem to be in the plastic container. Will reserve opinion of this kit when installed.
Was easy to install. I did have to correct a wiring error on the connector. Has been working fine for over a year.
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Scott
2/19/2026
No complaints at all. Great product