Solution for Charging Auxiliary Trailer Battery Through Truck's 7-Way Connector
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Question:
Hello! So i have been putting together the supplies ill need to wire up my 6x12 enclosed moto hauler/camping/work trailer. So far, I have a blue sea systems fuse block and a manually operated relay switch. I am going to pickup a 12V battery and extrerior mount box shortly. My questions are in regards to connection to the trucks main battery through the 7 pin connector. Currently, the trailer only has brake and running lights. I am planning to add lighting, 2 solar panels and charge contoller, a couple of usb ports and maybe setup for a in fan and dc powered fridge. I understand the operation and wiring up of the fuse block and load souces downstream but I need guidance getting from the trucks main battery to the aux battery through the current 7 pin connector.
asked by: Brent
Expert Reply:
In order to activate the 12V circuit on your truck's 7-Way so that you can maintain the charge on the trailer's auxiliary battery, you just need to run a length of 10 gauge wiring like # 10-1-1 (sold by the foot) through a breaker like # 9510 from the truck battery's positive post to the 12V pin on the 7-Way. This is the pin located at the 1 o'clock position (or 11 o'clock when looking at the backside/inside of the connector). Then from there you would wire the corresponding pin on the trailer's 7-Way to the auxiliary battery.
It's important to keep in mind though that this type of setup is only good for maintaining the charge on the trailer's battery, meaning it likely won't provide enough amperage to actually charge it up from a depleted state.
For the type and amount of accessories you're looking to power from the auxiliary battery, I'm wondering if a better option will be with a DC to DC charger like the Redarc # 331-BCDC1240D. This on-board system will actually boost the charge from the truck's battery so that you can charge up the battery during travel, ensuring that it's ready to go whenever you stop for work or play.
Redarc recommends using the 60-Amp MIDI Fuse Kit # 331-FK60 for protection and the Quick-Connect Set # BDW20047 will work perfect for creating simple plug-in connections.
I have attached the full installation guide below, along with a comprehensive video so you can see exactly how everything would be wired.

Product Page this Question was Asked From
Redarc In-Vehicle BCDC Battery Charger - Dual Input - DC to DC - 12V/24V - 40 Amp
- Battery Charger
- Battery Charger
- RV/Camper
- Trailer
- 200 Ah
- Charges/Maintains
- DC to DC
- 12V
- Solar Panels to Auxiliary Battery
- Vehicle Battery to Auxiliary Battery
- Redarc
more information >
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