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Discussion Starter · #1 ·
I'm trying to figure out how/where to connect the extra wires for a 7-way trailer connector wiring on my 2019 Subaru Ascent (Premium).

I am purchasing a pop-up tent trailer that has electric brakes, so am hoping to make things safer when towing. I found the brake controller connection under the dash, thanks to a couple posts on this forum, but am having difficulty finding the connections for such/a 7-way connector at the back of the vehicle.

I found this reply to a post with a PDF pointing out some OEM wiring harness diagrams, but was not able to decode them for exactly what I'm looking for. The immediate next reply to that same post shows a picture for a 7-way connector, where it uses all eight of the wiring harness plug pins, instead of just the five the flat four uses, but I have been unable to find one like that anywhere, only the flat four connector.

I bought a hitch from eTrailer and installed it myself, so I'm not a complete dunce, but I am having a heck of a time finding better information about where to purchase a 7-way connector that plugs into the wiring harness directly, or even how/where to connect the extra wires for the kind of 7-way connector that connects to an existing flat four.

Any input/expertise that can be provided would be greatly appreciated. I've begun losing my hair even faster than I already was after the unfruitful searches I've been performing for the past few days! :tango_face_wink: If further information would be helpful, please just let me know what and I will gladly reply.
 

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hitch wiring diagram

i'm trying to figure out how/where to connect the extra wires for a 7-way trailer connector wiring on my 2019 subaru ascent (premium).

I am purchasing a pop-up tent trailer that has electric brakes, so am hoping to make things safer when towing. I found the brake controller connection under the dash, thanks to a couple posts on this forum, but am having difficulty finding the connections for such/a 7-way connector at the back of the vehicle.

I found this reply to a post with a pdf pointing out some oem wiring harness diagrams, but was not able to decode them for exactly what i'm looking for. The immediate next reply to that same post shows a picture for a 7-way connector, where it uses all eight of the wiring harness plug pins, instead of just the five the flat four uses, but i have been unable to find one like that anywhere, only the flat four connector.

I bought a hitch from etrailer and installed it myself, so i'm not a complete dunce, but i am having a heck of a time finding better information about where to purchase a 7-way connector that plugs into the wiring harness directly, or even how/where to connect the extra wires for the kind of 7-way connector that connects to an existing flat four.

Any input/expertise that can be provided would be greatly appreciated. I've begun losing my hair even faster than i already was after the unfruitful searches i've been performing for the past few days! :tango_face_wink: If further information would be helpful, please just let me know what and i will gladly reply.
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2019 Ascent Touring (CWP)
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Why not see about buying the OEM rear harness via Subaru parts? It comes in the box if you would have bought the OEM hitch receiver instead of third party. I don't know if it's available separately or not, but it's worth investigating.
 

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Discussion Starter · #4 · (Edited)
The graphic is a step in the right direction, thank you for that. Now the only issue is the blue wire in the wiring harness plug at the back connects to one of the existing flat four connections. Another post said they mapped the thick red wire to the brake controller connection...I just don't know how accurate that is, since it doesn't look like a thick red wire connects to the brake controller connection at the front (However, the thick red wire is one of the wires not used by the flat four connector). **Edit: I found another graphic like this one that shows the black wire as the electric brake... Now I'm even more confused.

As for buying directly from Subaru, it would have cost more than twice as much for the hitch and wiring, not even counting installation, I price checked that a few days ago...Plus, I hadn't planned to be buying a trailer big enough to need brakes when I did everything and wired for a flat four. Oversight on my part, sure, but now I'm just trying to figure out where to wire things in the back, since the brake controller wiring is clearly already somewhere, since the plug is there under the dash.
 

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That's why I suggested you see if you can obtain the OEM rear pigtail that comes with the OEM hitch...it theoretically would be plug and play or at least provide you with an easier connection even if you need to connect it to another receptacle product.
 

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The graphic is a step in the right direction, thank you for that. Now the only issue is the blue wire in the wiring harness plug at the back connects to one of the existing flat four connections. Another post said they mapped the thick red wire to the brake controller connection...I just don't know how accurate that is, since it doesn't look like a thick red wire connects to the brake controller connection at the front (However, the thick red wire is one of the wires not used by the flat four connector). **Edit: I found another graphic like this one that shows the black wire as the electric brake... Now I'm even more confused.

As for buying directly from Subaru, it would have cost more than twice as much for the hitch and wiring, not even counting installation, I price checked that a few days ago...Plus, I hadn't planned to be buying a trailer big enough to need brakes when I did everything and wired for a flat four. Oversight on my part, sure, but now I'm just trying to figure out where to wire things in the back, since the brake controller wiring is clearly already somewhere, since the plug is there under the dash.

I wonder if the Ascent technical manual that can be downloaded on-line would have the information you are asking for. Alternatively, I would think your dealer could supply you with this information at no charge.
 

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Discussion Starter · #7 ·
That's why I suggested you see if you can obtain the OEM rear pigtail that comes with the OEM hitch...it theoretically would be plug and play or at least provide you with an easier connection even if you need to connect it to another receptacle product.
-- My apologies. I misunderstood your first post. I called my local dealer and that particular pig tail runs $236. Significantly more (And more than I would prefer to spend) than the $35 I could get the flat four plus 7-way converter. My hope was to find someone else that either found the pigtail for a 7-way somewhere else, or knew exactly which of the additional three wires to connect to which of the extra wires on the converter. If no one knows, I may just have to shell out the cash (Just hoping someone has encountered this before -- Just doing as much due diligence as I can before hand).

I wonder if the Ascent technical manual that can be downloaded on-line would have the information you are asking for. Alternatively, I would think your dealer could supply you with this information at no charge.
-- I've looked through a number of manuals, guides, and documents but haven't found the exact information needed. Another post links to a Subaru document with installation instructions for a hitch, but it doesn't really specify which wire is for what.

Either way, if nobody knows and I'm able to trace the wires successfully on my own, I will be sure to post the results for future eyes!
 

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The simple "converters" tend to only adapt the 4-pin pins to the 7-pin for a trailer that doesn't have a four pin and doesn't have brakes. (usually an older trailer before things got more standardized) You need all the signals present for full function including brake control with a brake controller plugged in up front. So hopefully you can ascertain where to get the signals from...

Unfortunately, this is one of downsides of using an aftermarket hitch solution...and not just for Subaru vehicles.
 

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Discussion Starter · #9 ·
The simple "converters" tend to only adapt the 4-pin pins to the 7-pin for a trailer that doesn't have a four pin and doesn't have brakes.
Understood, but the one I'm talking about converts the four to seven, but also has the extra wires for electric brakes and for power. Those wires are what I was referring to for where to connect them. I'm obviously going to have to splice, since no one seems to have the full pigtail wiring (Outside of Subaru), just hoping someone had encountered this before and knew the answer. Thanks for sharing your knowledge.
 

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I suggest you install a combination 4-pin and 7-pin termination at the back near your hitch receiver for best long-term results once you figure out the wiring mystery like the one in this kit:

https://www.etrailer.com/Wiring/Hopkins/HM40975-11998.html

Using an adapter provides an additional point of failure in the connection.

You could also consider using a wireless brake controller, but that may still be an issue without the fully active 7 pin connector.
 

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-- My apologies. I misunderstood your first post. I called my local dealer and that particular pig tail runs $236. Significantly more (And more than I would prefer to spend) than the $35 I could get the flat four plus 7-way converter. My hope was to find someone else that either found the pigtail for a 7-way somewhere else, or knew exactly which of the additional three wires to connect to which of the extra wires on the converter. If no one knows, I may just have to shell out the cash (Just hoping someone has encountered this before -- Just doing as much due diligence as I can before hand).


-- I've looked through a number of manuals, guides, and documents but haven't found the exact information needed. Another post links to a Subaru document with installation instructions for a hitch, but it doesn't really specify which wire is for what.

Either way, if nobody knows and I'm able to trace the wires successfully on my own, I will be sure to post the results for future eyes!
Hi D/O, I'm doing the same thing; a flat four Ascent-specific adapter and 7-way converter. Did you ever figure out the connections for the brake and 12v+ wires?

Thanks
 

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My current boat trailer is single axle, no brakes. I'm considering adding electric brakes. The Ascent included the factory hitch and has the flat and round receptacles wired up alongside the receiver. If I plug into the round brake receptacle will it trigger the brakes or does the Ascent require a brake controller added?
 

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I started with this 4 pin connector to my Ascent;
Basic 4-pin wiring harness

To that, I added this 4-pin to 4 and 7 pin adaptor;
Adapter

Then I took an ohm meter and figured out which pins on the Ascent's socket that the 4-pin harness plugged into were for the other 3 pins on the 4/7 pin adapter and spliced in.

Works great!
Did you run a separate 12v to the battery or are you using the 12v off the harness?
 
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