Can I Connect a 7 Way Trailer Plug When My Vehicle Only Has a 4 Way?
Updated 09/03/2026 | Published 08/29/2026
Question:
Can you use a converter connected from 7 pin to 4 pin if you don’t have a 7 pin plug only 4 pin
asked by: Richard S
Expert Reply:
Hi Richard, great question! If your vehicle only has a 4 way flat connector, you can use the Buyers Products Trailer Connector Adapter, part # 337TC1474P, to add a 7 way connector. You will need to ground the white wire to a clean, bare metal surface on the vehicle frame and run the power wire to the battery using 12 gauge wire, part # 12-1-1, with a 40 amp circuit breaker, part # 9510, installed before the battery connection. That will give you an active 12v circuit for charging your battery.
Just keep in mind that adding this adapter does not give you a brake controller or make the trailer brakes work. It can provide the trailer lighting functions and a 12 volt power circuit when wired as described, but if your trailer has electric brakes, you would also need to add a brake controller and the appropriate brake output wiring.
Are you connecting to a trailer with electric brakes, or do you just need the 7 way for the trailer lights?
Product Page this Question was Asked From
Buyers Products 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
- Buyers Products
more information >
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on Custom Fit Vehicle Wiring
Eric R.
9/3/2026
Hi Richard, I installed the 4-to-7-way adapter on my car. It doesn’t need the 12V supply wire if all you want to control is the lights. It even includes a 4-way plug if you want to use a smaller trailer. I had a problem about 1-½ years later, with water getting into the back of the adapter and causing a short, where both turn signals turned on at the same time. I hadn’t tried very hard to waterproof the wiring coming out of the adapter. I replaced it and used a lot of tape plus silicone caulk in the end where the wires come out. No problems since. Also, do yourself a favor and replace the supplied hardware with stainless steel. I had a hard time getting the first adapter out of its bracket because of corrosion on the screws. All-in-all, it is a nice way to get a 7-way connector for your trailer.