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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.

expert reply by:
Reno H
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Rich B.


On a 2011 Pilot does the 7 Way also control the trailer brakes on a 2020 RP-190 travel trailer?

Etrailer Expert

Chris R.


The 7-Way connector on your Pilot will have the brake output pin that carries this circuit, but you will still need to add a brake controller to actually send the power. Since you already have a 7-Way I recommend the Curt Echo # C51180, which will plug right into the 7-Way itself and pair to your smart phone.

Sean D.


i want to do the same. my trailer has a 7 pin and a brake box. i want to use battery for lights and usb charging at the track. i just want the TV to charge the trailer battery while we are traveling and not drain the tv battery while we are parked

Etrailer Expert

Chris R.


The above method will do a nice job of maintaining the trailer battery charge but the 12V circuit won't provide quite enough power to actually charge the battery up during travel. If you'll actually need to charge the battery your best option will be to add a DC to DC charger like the Redarc # 331-BCDC1225D, which will boost that charge and includes an isolator to cut off power when the truck is off.

Jason B.


@ChrisR would this connect to 7 pin/ 7pin fuse box?
Etrailer Expert

Mike L.


@JasonB The Redarc DC to DC charger would not use the trailer connector. We'll link you to an excellent install video that will explain the process for you. Just let us know if you have any questions.

Joe H.


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?

Patrick B.


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

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