How To Charge A Trailer Battery From Your Vehicle While Towing

Updated 10/21/2020 | Published 10/19/2020

Products Featured in This Question

Adapter 4 Pole to 7 Pole and 4 Pole w/Test Lamps

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Replacement In-Line Fuse Holder for Curt Wiring Harness - Qty 1

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$2.53

Deka Heat Shrink Butt Connector - 12-10 Gauge - Nylon Insulation - Yellow - Qty 5

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$7.49

Universal Installation Kit for Trailer Brake Controller - 7-Way RV and 4-Way Flat - 10 Gauge Wires

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Wiring Kit for Hydrastar Electric Over Hydraulic Actuators

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Question:

I have a 4 pin on my Subaru and small tear trailer with a 4 pin as well. Do not need brakes but I would like to charge the trailers battery while I drive. I think I would need to convert both the cars and trailers 4 pin to 7 pin. I think Id need a 4 pin to 7 pin adapter on the car-end and then a 7 pin with junction box on the trailer-end. Could I then run a wire from the black junction to t he battery to charge it?

asked by: Sam S

Expert Reply:

To easiest way to set up your trailer and vehicle to charge your battery would be to use the Trailer Wiring 7-Way Upgrade Kit w/ Junction Box and RV Style Connector Item # HS381-9000. This kit allows you to convert your trailers 4 pole to a 7 pole. The junction box comes with the 7 pole cable. You would just need to cut the four pole plug off, add ring terminals to the wires, and attach the wires from the trailer to the correct pins in the junction box. Including the wire that needs to run to your camper battery.

To convert your vehicle to a 7 pole I recommend the following items:

The 7-Way RV Upgrade Kit for Trailer Brake Controller Installation # ETBC7. Your current four pole plug connects to the four pole plug on the 7 pole adapter to provide light functions to your trailer. Since you are not needing the brake wire or reverse wire, those can be taped up in the bundle. The black and white wire are your power and ground. The white wire can be grounded anywhere on the frame as long as it is a clean piece of metal. The black wire needs to be extended up to the engine compartment, connected to a circuit breaker, then connected to the positive side of the battery.

A Replacement In-Line Fuse Holder for Curt Wiring Harness - Qty 1 Item # C58470-1 and a Curt 15-Amp Blade Fuse - Quantity 1 Item # C58450-1 on your power wire connected to your camper battery.

I recommend using Deka Heat Shrink Butt Connector - 12-10 Gauge - Nylon Insulation - Yellow - Qty 5
Item # DW05745-5 for the wire connections to your fuse holder