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Adding a Battery on an Enclosed Trailer to Power Interior Lights  

Question:

I want want to install a separate, standard 12 volt deep cycle trailer battery to operate my switched interior LED lights. The interior lights are wired to operate only when the ignition in my truck is on and trailer is plugged in. My current configuration is a breakaway battery perhaps I can eliminate this and use a larger battery for both lights and brakes?, 7 pin connectors on 2012 Toyota Truck and Featherlight 7x16. I will use a group 24 deep cycle battery on the tongue of the trailer. Can you tell me how I wire this and what parts I need?

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Expert Reply:

The best way to power the interior lights in your trailer is with its own independent battery. You will not want to use the breakaway battery. The breakaway battery is only designed to operate the breakaway and will drain extremely quickly, they're only required by law to operate your brakes for 15 minutes.

There's a few ways you can install a battery onto the trailer. One is to connect it to the 12 volt pin on the trailer's 7-way in place of the breakaway battery that is currently connected there, then connect the breakaway battery to the new battery. To do this you will need a new battery and some wire like # 10-1-1 which is sold by the foot.

Another is to use a junction box, like # 38656, and mount it to your trailer connecting all of the trailer wiring through it to your 7-way. This requires more rewiring but you end up with a nice, clean set up on the trailer once it's finished. You'll also need some ring terminals, # 44-5310A, to make the connections inside the box.

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Charles S
Josh H. profile picture

Josh H.

9/29/2024

Charles I want to be sure I understand this correctly. If I tie into the 7-way in place of the break away with a battery, it will both charge the battery from the vehicle and also send power from the battery to operate the trailers electronics (such as done light) when not plugged into the vehicle?

KevinC profile picture
Etrailer Expert

Kevin C.

9/30/2024

@JoshH The breakaway battery is solely for activating the brakes during a breakaway event and should never be used to power anything else. These batteries typically only hold a small charge that's enough to activate the brakes for 15 minutes so that you can get pulled over safely. Typically the trailer will have a "house" battery that stays on it and powers the 12v DC interior lights or other 12v accessories. If you don't have a battery on the trailer you can splice into the 7-way junction box and wire to your lights to the 12v accessory terminal, but you're limited to the amperage rating of that pin so you could potentially overload the circuit and blow a fuse on your tow vehicle. Running a wire from the 12v accessory pin to the battery would also send a charge to the battery, but you'd still be limited to the amperage rating of the circuit so the trickle charge you get really isn't the best battery charger.
Dean profile picture

Dean

10/28/2024

Should the battery in a break away brake system on a cargo trailer be the Positive side of a battery hooked to a white groundwire.And the ground wire goes directly to the frame ? Thank you For your anticipated response.

RobinH profile picture
Etrailer Expert

Robin H.

10/28/2024

@Dean your breakaway should have 3 wires and colors can vary. You probably have a black or red wire that will connect to the 12V power, white wire that connects to your main trailer ground, and a blue wire that connects to the brake output circuit. They typically come with instructions so I recommend following the installation instructions for your particular breakaway.

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