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


My truck is equiped with a 7 way plug. Is there any way I can use one of the leads to charge a battery in my trailer? Currently, the trailer has a flat four plug that I connect to the truck using an adapter. Any help is appreciated. Thanks,

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.

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i have a friend that wants to do this with his trailer that he takes to shows. he wants to use a battery in the trailer for lights while at the show but dosent want to draw his truck battery and doesnt want to have to unplug to avoid this. how should we wire his set up?

comment by: joe h - 2/18/2013

You will need a battery disconnect, check out part TD703.

Patrick B - 3/21/2013

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