How to Wire 12V Battery in Enclosed Trailer to Power Trailer Lights Independent of 7-Way Connection

Question

Question:

I have an enclosed trailer that currently powers the interior lights from the 12v black power wire on the seven way connected to the vehicle. I would like to add an auxiliary battery. Do I simply tap into the existing black power wire coming from the seven way and into the trailer into the new auxiliary battery and ground the battery to the frame. I know that the black power wire coming from the seven way to the auxiliary battery will keep and maintain the battery charge on the auxiliary battery but will this maintain the circuit and allow the interior lights to run even when the seven way is disconnected from the vehicle. Should there be any type of isolator between the batteries. Or would I be better to have the black power coming from the 12 V on the seven way go directly to the auxiliary battery to maintain the charge during travel and then when I arrived at my destination disconnect that wire coming from the seven way and connect the trailer black power wire to the auxiliary battery to power the interior lights to keep everything separate. Thanks

asked by: Jay C

0

Expert Reply:

You are correct in your description of how to wire in a new auxiliary battery in your enclosed trailer. You will take the 7-Way's 12V power feed and route this to the positive terminal on the auxiliary battery, and you will ground the second battery to the trailer frame, as you described. You might refer to the linked article on trailer wiring to see the usual wiring configurations on trailer connectors.

If you want to protect your vehicle battery from accidental discharge (such as if you left the 7-way plugged in without the engine operating) then you might consider an isolation solenoid, part # PK5231201. This provides a gate to control power flow from the tow vehicle's battery and is triggered by any ignition-controlled circuit. The linked photo shows how this simple device wires into your charging circuit. Either side terminal can be used as input or output, but the photo shows the left as input.

When the trailer is connected to the tow vehicle and you are running the engine a 12V maintenance charge will be delivered to the trailer's battery. This will maintain it but will not charge it if it is depleted. For a depleted battery you will need shore power and a charger like the CTEK # CTEK56353.

For your trailer's hot and ground battery wiring I suggest you use 10-gauge wire such as # 10-1-1 from Deka.

expert reply by: Adam R

0

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Ross M.

10/16/2024

Adam R., So to install the isolation solenoid, is there an "ignition controlled circuit" going to my trailer from the 7-way plug that I can access in my 7-way juntion box in my trailer? Or do I have to run a new wire from the engine bay back to the trailer? Thanks, Ross

Jameson C.

10/16/2024

@RossM If you wanted to install the solenoid on your trailer and have that circuit only active when the vehicle is on then yes you'd need to run a keyed power source back to it so that it would function like you want it to. Otherwise you could run the middle pin directly to the battery's positive post but put a switch on the wire so that you could manually turn it off and on. But at that point you may as well just bypass the solenoid and use a switch.

Answer 1

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,…

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Answer 2

If you are running a wire from the battery of your vehicle back to the 12 volt power circuit of a 7-way you will need to install a circuit breaker on the circuit like the part #9510. The advantage a breaker has over a fuse is that it will…

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Answer 3

There are a lot of people who run batteries on the interiors of their trailers without problems. What you can do is install a battery vent like part #A10-3300 on the trailer and it would be vented. Ideally you would have the battery sealed in a box…

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Answer 4

You will want to run the 12V wire from the 7-way trailer connector to the positive terminal on the larger battery. Then you will want to connect the larger battery to the breakaway battery from positive terminal to positive terminal, using 10 gauge…

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Answer 5

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…

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Answer 6

I can tell you exactly what you'll need to power your enclosed trailer's lights off of an independent 12V battery, though there isn't an adapter. You first need to mount the battery with a battery box for 12V batteries like #TLA7708R, and…

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Answer 7

To charge a battery for use in your trailer you will need to either use the CTEK MULTI US 7002 12-Volt Universal Battery Charger w/ Pulse Maintenance #CTEK56353 when you have your trailer parked, or use the Dual Battery Charger #331-BCDC1240D. The…

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Answer 8

Yes, in order to set your trailer up for use with shore power you will first need an AC distribution panel. For this, I recommend a Progressive Dynamics Series AC Distribution Panel. In order to bring power into the panel you will also need a power…

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Answer 9

When connecting two batteries together on an RV trailer you usually connect the batteries in parallel to draw 12 volts from both of the batteries. We have a photo, see photo at right, that shows how to wire the batteries in parallel. Once you have…

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Answer 10

You will need to use a circuit tester like #PTW2979 to find a wire in your 2015 Toyota Prius v that is hot only when you use your key (ignition switched power). When you do that you can simply wire in the Battery Isolation Solenoid #PK5231201, which…

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Answer 11

Although there are no hardware kits available to install the Polar Lock Side-Door Bar Lock Assembly #305736 we have found that you can use 5/16 inch carriage bolts along with some nuts and washers that are compatible with the bolts. All of which can…

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Answer 12

I recommend a 12 volt car battery rather than a breakaway battery because you may end up needing the larger battery down the road. What you will do is attach a battery box (see link for options) to the trailer frame. From the trailer side 7-Way…

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How to Wire 12V Battery in Enclosed Trailer to Power Trailer Lights Independent of 7-Way Connection

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