Third light brake light wire/brake controller for trailer

I have seen post on another forums about guys looking to install a trailer brake controller and need this particular wire.
I installed a pulse module for the third brake light and had to find it.
It is the light purple with a green strip, it can be accessed on the left cargo panel.
Attached is a picture of it.
Don’t ask me how I found the ground for the third light, it was pure luck

 

Picture with module

 

Good info, thanks for posting.