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Everyone,

recently installed the Curt #56040 trailer wiring harness to my 2020 Outback. I am having an issue where the trailer lights are constantly remaining on, even when the vehicle lights are off, and the car is parked, engine off, and locked.

Trailer is a brand new Aluma with LEDs.

Does anyone know what the problem could be?
 

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2020 Subaru Outback Premium
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29 Posts
It sounds like the plug wiring is not correct for your trailer. You need a test light to see if the wires are in the right position. The wires should be easy to reposition inside of the trailer plug.
 

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On canbus systems the electrical system tests the circuit for continuity with a small voltage signal that can be enough to illuminate a non-canbus LED Use a DVOM to test the circuit you will likely see 9v when lights are off. If using a test like it has high enough resistance to pull that 9v to zero and the incandescent test lamp will not illuminate. The odd thing for me is car and lights off and their still on. This is not what I would expect. Do they time out and go off after 10 to 20 minutes as in computer delayed shut down of the system?
 

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2020 Outback Limited
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122 Posts
When the car is running, do all the trailer lights work properly? Turn signals, left and right working? Brake lights when brakes applied?
 

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Does anyone know what the problem could be?
Only a question: Are you using a trailer wiring adapter box between the 8-pin trailer connector in the cargo area, and the 4-pin connector at the trailer? If so, do you know the make and model? Is it the right one for the 2020 Subaru Outback?

When using an adapter, the car and trailer wiring are isolated. In order for the trailer lights (I presume clearance and tail lights are the topic) to remain on when everything else is off, the adapter circuit would have to be involved. It might not be the correct one, or is faulty.

The trailer adapter has it's own 12 V power supply from a fuse in the car. When the car's tail lights are turned on (with the headlight switch), the adapter's connection (through the 8-pin connector) to the tail light circuit signals the adapter to turn on the trailer tail lights. The power for the trailer tail lights, however, comes from the 12 V supply; not from the car's tail light circuit. When the car's tail lights are Off, the adapter should not be passing power through to the trailer tail lights.

If you're not using an adapter, and have wired the trailer connector directly to the car's wiring (e.g., to the 8-pin connector), then it might be miswired.
 

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2020 Outback Touring XT
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11 Posts
Everyone,

recently installed the Curt #56040 trailer wiring harness to my 2020 Outback. I am having an issue where the trailer lights are constantly remaining on, even when the vehicle lights are off, and the car is parked, engine off, and locked.

Trailer is a brand new Aluma with LEDs.

Does anyone know what the problem could be?
Can't help with your problem but hope you can help with mine. I'm trying to install the same Curt 56040 harness in my '20 Outback Touring XT. I can't locate the vehicle wiring harness that the 56040 should plug in to. It doesn't seem to be where Curt's instructions say it is, tucked up behind the driver's side interior wall panel near the back of rear seat. Where'd you find it? Thanks!
 

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It doesn't seem to be where Curt's instructions say it is, tucked up behind the driver's side interior wall panel near the back of rear seat
It should be on the right (passenger) side, under the floor panel above the right front corner of the spare wheel well:
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Everyone,

recently installed the Curt #56040 trailer wiring harness to my 2020 Outback. I am having an issue where the trailer lights are constantly remaining on, even when the vehicle lights are off, and the car is parked, engine off, and locked.

Trailer is a brand new Aluma with LEDs.

Does anyone know what the problem could be?
This happened on my old Dodge with a Curt trailer light box. It was always the box. Call Curt to warranty a replacement. The circuit board gets stray current from corrosion or bad grounds and it gets fried.
 

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2020 Outback Touring XT
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Thanks to all those who responded! Y'all are correct and Curt's instructions are wrong. After viewing a 'how to' video, I found the needed plug, tucked in to the right-rear corner of the spare tire compartment, under the floor in the back of my Outback. **** Curt's incompetence caused me to waste a couple hours and a very sore back this afternoon, removing most of the interior panels on driver's side, behind the rear seat, looking for the plug their instructions said were there, but wasn't. I'll be sending Curt a 'nastygram' in the near future.
 
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