2015 trailer brake controller

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mikevg

Member
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Mazda CX-9
Hi all, newbie here,

I have a 2015 CX-9 that I'm looking to install a trailer brake controller in. I'm wondering if others have done it before and have any tips/recommendations on where to install the controller and how to run the wiring?

I've already installed a 7-pin receptacle and wired it into the factory 4-pin receptacle, but I'm needing to install the brake controller and run the wires back from that, and power from the battery.

From the looks of things underneath it doesn't seem like there's any way to run wires back easily, so I'll probably have to run them through the cab and drop down through the trunk somewhere, so I'm just wondering if someone else has already done this and might have some tips or warnings.

Thanks!
 
Gotta ask, how heavy of a trailer do you plan to pull?
I know having brakes on a light trailer can help (especially in mountains), but at only 3500lbs max weight you shouldn't need it.

You also have to keep in mind the GCVW of 8560(ish). So even though the rating is 3500# ypu may not legally be able to pull that much once you load the vehicle with people and gear.
 
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Some states have trailer brake requirements as low as 1000#, some 1500#, a few at 2000#, many at 3000#.

Do get a proportional trailer brake controller, not the old fashioned time delay controller nor the pendulum controller than needs to be manually leveled.

You'll need +12v to the controller and +12V to the 7-pin plug. Do run the adequate size ground wire from the brakes through the 7-pin plug all the way to the battery negative post. Don't rely on chassis ground for anything as important as electric brakes. Avoid wire nuts. Good crimp connectors are OK. Soldered & heat shrink are best.
 
Thanks guys. I already have a tekonsha p3 that I took out of my 3/4 ton truck when I sold it. I'm really just looking for tips on locating the controller and running the wiring as everything in the mazda is a lot tighter than my truck was, and I don't want to unnecessarily tear anything apart trying to figure out how to install it.
 
Scott91370 said:
You also have to keep in mind the GCVW of 8560(ish).
Click to expand...

Where are you finding that number at? I can't for the life of me find a GCWR for this vehicle anywhere. Only that it's "max towing" is 3500 lbs. According to the door sticker it's GVWR is 5997 lbs, and combining that with 3500 towing tells me 9497 lbs. If the GCWR is actually lower I'd like to know, but it doesn't seem that anyone lists this anywhere. Even the door sticker doesn't have that information.
 
My manual has the ratings on 4-14 and 4-15

image_zps5fkp8mwh.jpeg
 
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I ended up running the wires for the brake and charge inside and down through the same grommet as the factory 4 pin. The door sill trim popped up fairly easy and offered a decent amount of room to tuck the wires in. The controller was mounted to the panel under the dash right next to the hood release. It was a tight fit and the hood release makes light contact with the bracket when releasing the hood. I ran power feed and ground wires through the firewall in the same grommet as many other wires from under the dash. These were connected to the battery through 2 circuit breakers I purchased ( I believe it was a 20A for brakes and 30A for charge). I attached the ground to the same bolt the attaches the battery ground to the chassis using a ring terminal. The wiring diagram I have shows the Green/Yellow wire for the brake pedal connection and I believe this is what I connected the controllers signal with.
 
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