Cx-9 2018: Brake controller vs Emergency braking system

barter

Member
Hi,

I have a cx-9 signature 2018. I want to install a brake controller for my pop up trailer with electric brakes.
All brake controller instructions I found are telling us to wire to brake pedal signal.

I think it's not suitable for this car since it would not pickup brake signal when cruise control is automatically braking the car. Same issue with automatic emergency brake system.

This could result in trailer jack knife if car is automatically breaking hard and trailer brakes are not applied.

I found suggestion about tapping the center brake light signal instead of brake pedal signal. Anyone know how to Hook to the center brake light signal from the dash area? I don't want to run a wire back from tail gate to brake controller for this purpose.

Thanks.

FranK.
 
I think all the brake lights illuminate when automatically braked, correct?
If so, how does that signal get to the lights?
Is there a conventional switch activated by the brake pedal arm, or where does the brake light power come from?
If there is a conventional switch on the brake pedal arm, is that wire energized when the adaptive cruise control activates the brakes?

You're making a lot of assumptions. It's time to do more investigating.

If all else fails, do not use the adaptive cruise control when towing. Use the conventional cruise control.
 
Correct, all brake lights are illuminated when the brakes are applied during adaptive cruise. With this in mind the signal to the lights is probably controlled by the ECU and activates when the ABS pumps are energized when braking.
 
If you have enough understanding of technical wiring diagram, you can check out this thread.https://www.mazdas247.com/forum/showthread.php?123859597-2016-TC-CX9-Workshop-Service-Manual

There is almost the full technical wiring diagram posted for the CX-9, but I had a very quick look and couldn't find the brake lights wiring diagram, but you may have more luck than me. Interestingly, according to the wiring schematics, there is a wiring diagram call Trailer Tow (0918-14), but i believe it is one of the diagram that the OP didn't have the time to scan and post. There would also be a wiring diagram for the center brake light (0918-7,8), but that one isn't up either. You may be able to ask for those specific diagram on that post.

I don't have experience with brake controller, but aren't you already wired into the brake light systems for your trailer brake light through your hitch cable ? That would be simpler than trying to wire to the center light (although this would still be in the back of the car).
 
I have NOT yet downloaded the remainder of the wiring diagram for publication. I've been really slammed at work.

When I installed my brake controller, I DID run an additional wire from the rear of the vehicle to the front. I installed a 7-Pin trailer connector. This has an independent ground and +12v line direct to the CX-9's fuse box, along with the brake controller signal.

I'm using the OEM Trailer light kit, Part Number 0000-8E-N30 with the 4-Pin connector cut off and spliced into the 7-Pin connector. I tapped the brake light signal from the input to that unit. (I am not making any modifications to the CX-9's factory wiring harness and instead modifying the add-on module.)

In total, I have run a total of FOUR wires from front to rear of the CX-9 (By way of the passenger side under-door trim) +12 Volts and Ground from the engine bay, the brake signal from the controller to the trailer, and the brake light signal from the CX-9 to the trailer brake controller.

I also have four wires that enter the engine bay from the passenger compartment. +12 Volts and Ground for the trailer itself and +12 Volts and Ground for the trailer brake controller. I'm using #10 AWG wire (5.26 mm^2) wire for a 30 AMP capacity. Overkill, but it works.

I'm using a Tekonsha Prodigy P3 brake controller.
 
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