Trailer Wiring for 2025 Subaru Ascent that Can Also Charge a Trailer Battery
Updated 09/12/2025 | Published 08/20/2025
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Question:
Hello, I have a question about the wiring for a 2025 Subaru Ascent. I am leaning toward using a 4 pin connector because you recommend them and for ease of use with any trailer. For my camper, though, Id ideally like to add some wires to be able to charge a battery. Would it be possible to add a pin into the connector to allow for wiring up a separate 2 pin connector for 12V auxillary power? Alternatively, is there a 5 pin wiring harness that includes this already?
asked by: Justin C
Expert Reply:
Hey Justin, for trailer wiring that you could use to charge a battery you would need to convert to a 7-way from a 4-way. The exact kit you'd need for that is the part # ETBC7L which comes with everything needed for that.
For a 4-way to start you'd want the part # C56040 which installs easily.
So the reason you don't want to use a 5-way is that the fifth pin of a 5-way is designed for a reverse light signal circuit so it doesn't ever have a very heavy gauge wire associated with it so it wouldn't be able to really charge a battery. The 12 volt circuit of a 7-way has a much heavier gauge wire which can carry the additional amperage.
How big of a battery do you have?
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Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
- Custom Fit Vehicle Wiring
- Trailer Hitch Wiring
- Vehicle End Connector
- Powered Converter
- No Tow Package
- 4 Flat
- Plug and Lead
- Plug-In
- Hidden
- CURT
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Jameson C.
9/12/2025
Hey Justin, did you have a chance to convert to a 7-way setup for your camper battery charging? I'd love to know how it worked out for you, as it could help others looking to do something similar.