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Discussion Starter · #1 ·
I have a Tekonsha P3 brake Controller. It came with both an unterminated vehicle side cable as well as a Subaru Specific cable with connectors on both ends. I noticed that the unterminated Subaru supplied cable has a 20 Amp fuse in the blue wire to the trailer brakes. The cable with both connectors does not have a fuse and all wires are the same size which I believe are 14 awg. Does the wire to the brakes need to be fused or is it safe to use the cable without the fuse? Is the 12 volt power to the brake controller separately fused? Any help would be appreciated. I plan on towing a single axle trailer less than 2900 lbs loaded.
 

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2019 Ascent Touring (CWP)
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Just use the pre-terminated Subaru specific cable as-is. There's no need to add anything. That's how I ran it in my previous vehicle and if I installed it in my Ascent (no need to do so), I'd do it the same way. Plug and play is my thing. There is more discussion on brake controllers in the forum's Towing discussion area, too.
 
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I don't know the answer to whether or not the harness needs a fuse or not but I bought the P3 controller and the specific adapter harness and just plugged it in and went. Zero problems. Couldn't be easier.

The hardest part of the setup was figuring out how to mount the brake controller.
 

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Discussion Starter · #4 ·
I sent an email to SOA to see what their response is. Haven't heard back but I did see there is a fuse, #28, in the inside fuse box labeled Trail so if this fuse feeds the controller power, having a 20 Amp fuse going to the brakes is not going to do much if it's protected by a 15 Amp fuse. Maybe someone with a wiring diagram can verify that this fuse does indeed feed the controller.

I placed a strip of 1 1/2" wide velcro across the shelf to the left of the steering wheel and the velcro mate lengthwise on the controller. It sits in the shelf snuggly and the manual level is still accessible. The per-terminated Subaru specific cable is just long enough by going down along the steering column and over to the vehicle harness connector.
 
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