Recommended 7-way Connector For 2020 Subaru Outback With 12v Power For Trailer Battery

Updated 01/31/2026 | Published 04/20/2021

Products Featured in This Question

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(3445)

$42.20

No-Drill Mount for Electrical Mounting Bracket - Short

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$24.05

Autowbrake Electric Brake Controller - Trailer Mount w/ Remote Fob - Up to 3 Axles - Proportional

(105)

$479.99

7-Way RV Upgrade Kit for Trailer Brake Controller Installation - 12 Gauge Wires

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Question:

Dear Expert at ETrailer: I bought a 2020 Subaru Outback, had dealer put a trailer hitch and a 4 pin wiring port in the bumper cover on it. Then I got a Scamp trailer, and I want to put electric brakes on it, and I want to be able to charge the Scamp’s battery. So I want to add a 7 pin connector to the Outback, apparently from what I read, with a wire running to the Outback battery. I would like to still have the 4 pin plug available for my boat trailer, so unless there is some reason I am not aware of, I would like to keep the two connectors separate. I want to use the wireless brake controller AuTowBrake, as that is what Scamp is now using. Should could? I splice wires into existing 4 pin harness? What is the best harness for my particular situation? Thanks for your advice.

asked by: Jeff C

Expert Reply:

To add a 7-way connector to your 2020 Subaru Outback I recommend the # ETBC7L which will plug into your existing 4-way connector and will only require you to make two connections, grounding the white tire to the frame of your vehicle, and running the black wire to the battery of your vehicle with the included 40 amp circuit breaker. This will work perfectly with your Autowbrake Electric Brake Controller # 3430001 and give you the 12v auxiliary power you need.

This will give you the 7-way you need for your Scamp trailer and will still have a 4-way connector when towing your boat trailer.

To mount the # ETBC7L to your trailer hitch receiver you may also need no drill mounting bracket # 18140 unless your hitch has a built in mounting bracket.

I included videos of the products for you to take a look at.

expert reply by: Samuel C

Tom

1/30/2026

I have the same situation (Subaru with existing four pin wiring, plan to tow a Scamp with wireless Autowbrake). But I need a little better explanation of the ETBC7L adapter. My understanding is that to be able to charge the trailer battery while driving, I need a wire to the car battery. It looks like that is the black wire in your diagram. But the yellow wire is also labeled as being for 12V power. What's that yellow wire for? What would it connect to? Why are there two wires for 12V power? Very confusing. Also, your diagram says the blue wire is for the brake controller. But Scamp's instructions specifically say "the blue brake controller wire is not needed for the Autowbrake system." So what's right and wrong here? Do I hook the blue wire up to something or just tie it off somewhere? Again, very confusing. Are there better instructions printed somewhere? I am handy and can do an installation, but I'm not going to guess which wires go to what. Thanks.

Samuel C.

1/30/2026

@Tom The black wire is the only wire you need, it is the 12v power circuit, which is why the ETBC7L comes with a single wire and circuit breaker to attach to the battery of your car. The blue wire would be used if you had a traditional brake controller, which you do not. The yellow wire is not 12v power, it is either reverse lights or some trailers use it as an auxiliary circuit (it is left unused on 99.9% of trailers). We do not have any other instructions. You plug a 4-way connector into the 4-way connector portion on the back of the 7-way included in the ETBC7L, Ground the white wire to the frame of your vehicle, and connect the included black wire to the black wire on the back of the included 7-way, running it to the battery on your vehicle with the included circuit breaker. That wire will power your AuTowBrake controller, and runs to the battery on your trailer to keep it from going dead.

Tom

1/30/2026

@SamuelC Great. Thanks, so the extra yellow wire and the blue wire will just get tied off; I don't use those. Thanks again!