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I have a dealer installed tow package and I purchased the Tekonsha P3 brake controller as per many recommendations on this forum (THANKS!). However I am stuck with the wiring. I have attached a photo of what I am currently dealing with. I found where to connect the Subaru-provided pigtail for brake contollers on the driver's side by the footrest (oddly enough this seemed to be where most people struggled but for me it was easy to locate). The pigtail itself has 4 wires coming out (Blue, Black, Red and White). However, the blue wire seems to have a fuse connected to it encased in a small black box that has a hole where you can screw it to attach it to something? Where do people screw this down or how do they hide it? Does that little black box need to be securely attached to something? Am I correct that this is a fuse?

The Tekonsha P3 came with a pigtail as well with 4 wires and holy-wow the colors match up with the Subaru provided pigtail! Even I can't screw that up! However, the sizes (gauges) of the wires do not match up and the provided butt connectors seem like they will not work for proper splicing. Also I have been told it is not a good idea to splice 2 wires together of different gauges regardless of the method (butt connectors or soldering). Here is what I'm dealing with in a nutshell:

SUBARU Wire Sizes:
Blue Wire: 14 AWG
Black Wire: 16 AWG
White Wire: 16 AWG
Red Wire: 16 AWG

TEKONSHA Wire Sizes
Blue Wire: 12 AWG
Black Wire: 12 AWG
White Wire: 16 AWG
Red Wire: 16 AWG

Tekonsha only supplied me with 4 butt connectors based on the size of their wires. I have 2 that are for 10-12 gauge and 2 that are for 14-16 gauge. However, the black wire in particular I would be splicing a 16 gauge to a 12 gauge with a butt connector rated for 10-12 AWG!? This seems like a bad idea? If I used the Tekonsha supplied butt-connectors it seems this would result in a very loose crimp on the Subaru 16 gauge wire side. Any help regarding the safety or how to splice the wires regarding the differences in size would be much appreciated.

My other option is to purchase a Tekonsha Plug-In Wiring Adapter for Electric Brake Controllers that is rated to fit the Ascent. I found one on eTrailer that is confirmed but my issue now is that it appears there is no fuse thingy similar to the one on the pigtail that was supplied by Subaru. How important is that thing? Is this really a correct/safe adapater if it doesn't include the black fuse box thingy? I have supplied a screenshot of this online adapter part as well.

Thanks in advance for any help on the proper way to get my p3 wired up.
 

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I used the Tekonshia pre-terminated cable in my Grand Cherokee with no issue for 7 years and it also had no protective fuse. I'd do the same in my Ascent if I ever need to use my P3 in it.
 

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I have a dealer installed tow package and I purchased the Tekonsha P3 brake controller as per many recommendations on this forum (THANKS!). However I am stuck with the wiring. I have attached a photo of what I am currently dealing with. I found where to connect the Subaru-provided pigtail for brake contollers on the driver's side by the footrest (oddly enough this seemed to be where most people struggled but for me it was easy to locate). The pigtail itself has 4 wires coming out (Blue, Black, Red and White). However, the blue wire seems to have a fuse connected to it encased in a small black box that has a hole where you can screw it to attach it to something? Where do people screw this down or how do they hide it? Does that little black box need to be securely attached to something? Am I correct that this is a fuse?

The Tekonsha P3 came with a pigtail as well with 4 wires and holy-wow the colors match up with the Subaru provided pigtail! Even I can't screw that up! However, the sizes (gauges) of the wires do not match up and the provided butt connectors seem like they will not work for proper splicing. Also I have been told it is not a good idea to splice 2 wires together of different gauges regardless of the method (butt connectors or soldering). Here is what I'm dealing with in a nutshell:

SUBARU Wire Sizes:
Blue Wire: 14 AWG
Black Wire: 16 AWG
White Wire: 16 AWG
Red Wire: 16 AWG

TEKONSHA Wire Sizes
Blue Wire: 12 AWG
Black Wire: 12 AWG
White Wire: 16 AWG
Red Wire: 16 AWG

Tekonsha only supplied me with 4 butt connectors based on the size of their wires. I have 2 that are for 10-12 gauge and 2 that are for 14-16 gauge. However, the black wire in particular I would be splicing a 16 gauge to a 12 gauge with a butt connector rated for 10-12 AWG!? This seems like a bad idea? If I used the Tekonsha supplied butt-connectors it seems this would result in a very loose crimp on the Subaru 16 gauge wire side. Any help regarding the safety or how to splice the wires regarding the differences in size would be much appreciated.

My other option is to purchase a Tekonsha Plug-In Wiring Adapter for Electric Brake Controllers that is rated to fit the Ascent. I found one on eTrailer that is confirmed but my issue now is that it appears there is no fuse thingy similar to the one on the pigtail that was supplied by Subaru. How important is that thing? Is this really a correct/safe adapater if it doesn't include the black fuse box thingy? I have supplied a screenshot of this online adapter part as well.

Thanks in advance for any help on the proper way to get my p3 wired up.
I used the wiring that came with the P3, soldered them to the Subaru-supplied harness, and then put shrink tube over the soldering points. Didn't notice the wire size difference, and it works fine. As far as the small black fuse box, I didn't attach it to anything as the bulk of the wiring, once wrapped in electrical tape, is coiled up on itself as I mounted the brake controller, using the detachable mount, on an extra fuse dash cover that places the brake controller, when mounted for towing, only a few inches away.
 

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I'm trying to locate the plug in for the wring harness that Subaru supplied up under the left kick plate. That harness has a box shaped white connector and all I see under the left side of the brake pedal when I contort myself in there is a longer, rectangular shape white connector. I cant see any of the photos other people say they've posted showing where to look at it.
Thanks
 

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I'm trying to locate the plug in for the wring harness that Subaru supplied up under the left kick plate. That harness has a box shaped white connector and all I see under the left side of the brake pedal when I contort myself in there is a longer, rectangular shape white connector. I cant see any of the photos other people say they've posted showing where to look at it.
Thanks
The pigtail should have been put in your glove box or in the storage bin in the cargo area. It is not connected to the plug under the dash, because it needs the non-plug end to be wired to a controller first.
 

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@SRS Well have you tried to plug the 2 white ones together? Because sounds to me you've found everything!
Here is in pictures what Robert explained above:
The 'longer, rectangular shape white connector' when you contort yourself ;) is the male end found under the dash in the lower left corner:

526


Your 'harness has a box shaped white connector ' is the female end harness, comes supplied loose with your OEM hitch:

527


And then you connect the wires of that loose end to the wires of your Brake Controller:
528


Let me know if you have any other questions. I just all learned and did this myself. Prior 'a harness' to me was something you wear on your hips to climb on rock or a mountain ?
 

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I cant find the square white one under the dash that matches the square white plug of the pigtail (wiring harness). What I find under the dash is longer and skinnier white plug in but not the square one shown in these pictures.
Also, this forum says i need 1000 mile on ascent before towing but the dealer said 500. Thoughts?
 

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I cant find the square white one under the dash that matches the square white plug of the pigtail (wiring harness). What I find under the dash is longer and skinnier white plug in but not the square one shown in these pictures.
Also, this forum says i need 1000 mile on ascent before towing but the dealer said 500. Thoughts?
  • Absolutely 1000 miles. They are incorrect.
Regarding the harness...
Can post a pic of what you see behind the dash?
 

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  • Absolutely 1000 miles. They are incorrect.
Regarding the harness...
Can post a pic of what you see behind the dash?
I installed the P3 controller, using the the Subaru supplied harness and the supplied P3 harness connecting with butt connectors. The following Pics show under the dash wo trim removed, trim removed, highlighting connector, and completed job
IMG_2293.JPG
IMG_2294.JPG
IMG_2296.JPG
IMG_2299.JPG
IMG_2305.JPG
 

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Maybe someone posted this already but etrailer has a specific adapter for the ascent item# 3062-P. It will connect to the brake controller to the existing connector assuming you do have the tow package installed from the manufacturer.
 

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Maybe someone posted this already but etrailer has a specific adapter for the ascent item# 3062-P. It will connect to the brake controller to the existing connector assuming you do have the tow package installed from the manufacturer.
That's actually a Tekonsha product so it may be available elsewhere also.
 

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Hey guys just installed my P3 controller. Picking up the trailer this weekend. Just thought I’d share how I mounted it. I heard some people using fuse door but had to reinforce. I used the blank boxes. Very secure. I’m short so it doesn’t get in my way. Hope this helps.
 

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@xydadx3 I sat in the seat and it’s ok. Driving will be fine. I like that it is higher up so I can see and have access to without drilling holes into the dash. I just have to be cognizant getting in and out of the car. I plan on just leaving the small bracket on in like the first picture when I’m not using it. I will be painting the screws black so it’s more incognito.
 

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Just curious to know if the factory supplied pigtail harness is preferable to the Tekonsha preface for the Ascent, I assume it would be because of the in line fuse. What have the majority of users gone with ?
 

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Just curious to know if the factory supplied pigtail harness is preferable to the Tekonsha preface for the Ascent, I assume it would be because of the in line fuse. What have the majority of users gone with ?
I went with Tekonsha Ascent specific adapter, was plug and play. I wouldn't worry about the fuse as long as you are using a Tekonsha controller and keeping the peak braking voltage in spec (listed in manual, can't remember off the top of my head).
 

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I would be comfortable using it either way.
Out of convenience mostly I used the factory pigtail to the vehicle and spliced in the tekonsha connector.
Same here. Especially with the one to one color match. Either way works though.
 

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I decided to go with the factory pigtail spliced to the factory plug and everything went just fine, thanks for your input. Now when all this Covid-19 settles I can hopefully pick up my new travel trailer that’s in limbo at the RV dealer.
 

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Sorry for my naiveté, I just installed my hitch and I thought I simply needed to install the 7 pole adapter from the factory adapter in the rear of the vehicle to the 7 pole adapter kit like the
Tekonsha OEM Replacement Vehicle Wiring Harness with 7-Way Trailer Connector
Item # 118290

Dont some trailers have preinstalled brake controllers? Which would mean you do not need to install a separate one?

Thanks
 
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