How to Make Additoinal Connections on a 4-Way to 7-Way Trailer Adapter

Question:

Hello there. We just bought a kia sorento with a 4 way prong attached to the hitch. We want to pull our pop up 1700lbs with a 7 way adapter plug. The pop up camper does have brakes. I have the part we need....4 way to 7 way with wires. I just dont understand HOW to wire the three extra wires. I know that the white wire is the ground wire and needs to attach to the frame of the car. How do you wire the other two? Help!

asked by: Michael

Expert Reply:

To complete the install of a 4-way to 7-way adapter like part # 37185 you need to ground the white wire to the vehicle's frame like you mentioned, connect the purple wire to your vehicle's reverse light circuit which you can usually find behind the tail lights, connect the black wire to the vehicle's battery through a 40 amp circuit breaker, part # 9510, for a 12 volt power source, and connect the blue wire to a brake controller installed in the vehicle's cab to power electric trailer brakes. These connections give you a fully functioning 7-way trailer connector. Our # 5506 kit includes the wiring and circuit breaker to make all the additional connections.

If you don't need every function of the 7-way you don't actually have to connect every wire and can just cap them off. The only one that must be connected is the ground wire. A lot of trailers don't have reverse lights so the purple wire is often not used. Sometimes the blue wire isn't needed if the trailer doesn't have brakes and the black wire isn't needed if the trailer doesn't have a battery or anything else needing 12 volt power.

Since your trailer has brakes you need a brake controller. Traditionally you run the blue wire into the vehicle's cab and connect it to a brake controller like the Prodigy P3, part # 90195. You also likely need to do some additional wiring inside the cab to install the brake controller. Instead of using a traditional controller in the cab I recommend capping off the blue wire and using the Curt Echo, part # C51180. It plugs into the 7-way and instead of installing in your cab and it's controlled by your smartphone. It doesn't require the brake circuit (blue wire) to be active at the 7-way. It does need 12 volt power via the black wire so you do need to connect it to your vehicle battery through a circuit breaker. The breaker again is part # 9510 and you can use # 10-1-1 for wiring. I've linked an article to help you route the wire through the vehicle to the battery.