How Do I Connect a Trailer with a 7 Way Plug to a Vehicle with a 4 Way Flat?
Updated 07/04/2026 | Published 06/28/2026
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Question:
I have a 7 way round plug on the trailer. Need to go to a 4 way flat on vehicle. Any suggestions
asked by: Ron H
Expert Reply:
Hi Ron, you can definitely do that, but the right solution depends on whether your trailer uses all seven functions or just the basic lighting.
If you only need the running lights, brake lights, and turn signals, the Curt Trailer Connector Adapter, part # C57672, is a great option. Your vehicle's 4 way flat plugs into the adapter, and your trailer's 7 way plugs into the other side. By grounding the adapter, you'll have the basic 4 way lighting functions without needing to wire in the additional circuits.
One thing to keep in mind is that if your trailer has a 7 way connector because it has electric brakes, a simple adapter won't allow the brakes to function. In that case, you'll need to install a fully functioning 7 way on your vehicle along with the appropriate brake controller wiring. The Universal Installation Kit, part # ETBC7, includes the wiring and 7 way connector needed for that type of setup.
Can you let me know if your trailer has electric brakes? What brake controller are you planning on using, if so? That will determine how much wiring you need to do.
(click to enlarge)
Larry
7/3/2026
My trailer was wired for electric brakes but my vehicle just had wiring for a 4 way. I also installed an AutowBrake controller on the trailer wired into the standard light circuit for the vehicle and it gets its power by using my headlights and everything on the trailer works. This kit also has the 4 way connector also
Chad
7/3/2026
When you say 7 pin round connector on the trailer are you referencing the shape of the plug or the pins? Because there is such a thing as 7 pin agricultural connector that uses round pins. Just google “7 pin ag connector” and 7 pin rv connector” to see the difference. I’m guessing it’s 7pin Rv but wanted to clarify. I have used this ETBC7 adapter and works fine. If you just need the basic 4 pin connections it’s overkill but is an easy way of having both on your vehicle and gives you connections if you want to add a brake controller. Other options is just putting a 4 pin pigtail on your trailer if all your ever going to hook up is 4 pin. Just be sure to shrink tube or liquid tape any connections to keep corrosion out of wires. I’ve see salt corrosion ruin harnesses for feet from people using scotch locks.
Product Page this Question was Asked From
Curt Trailer Connector Adapter - 4-Way to 7-Way RV and 4-Way Flat
- Custom Fit Vehicle Wiring
- Wiring Adapters
- Universal Fit
- 4 Flat to 4 Flat
- 4 Flat to 7 Blade
- Plug and Lead
- CURT
more information >
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Ron H.
7/2/2026
Awesome thanks Heather, my trailer only has lights turn signals and brake lights. The seven way is only wired that way so this adapter that you mentioned will work perfect thank you. Ron.