Can I Charge My Trailer Battery Using 7-Way Trailer Connector on Truck

Expert Reply:

You would not be able to charge your battery through the wiring on your 4-way trailer connector. Since your truck has a 7-way connector, you could maintain the power to the battery but not charge it.

To begin, you would need to cut off your 4-way trailer connector and install a 7-way connector on the trailer like the Optronics 7-way, part # A7WCB. You would need to connect the appropriate wires. White is ground, Yellow is left turn and brake, Green is right turn and brake, and Black is the hot lead that you will tap into later. If your trailer does not have brakes or reverse lights you would not connect these pins (see picture).

To maintain power to the battery, you would need to run a wire from the positive terminal on the trailer battery to the power wire on the 7-way. I would recommend using 10 gauge wire, part # 10-1-1, and connecting to the Black wire on the trailer 7-way, or the pin in the 11 oclock position when looking at the front of the connector to the positive battery terminal (see FAQ). You would then connect the negative terminal to a clean metal surface on the trailer frame for a ground connection.

I have linked an FAQ on wiring and a diagram showing the wiring pin out for the trailer side 7-way.

expert reply by: Reno H