If you installed a brake controller with a plug to match the plug under the dash the brake controller will light up when you put on the brakes. But as I said above the blue wire from the plug under the dash will stop at the safety wall so the trailer brakes will not work.
As you can see in the photo below pin #2 is missing on the engine side of the safety wall.

You will have to put a pin in pin #2 and then run that wire to the plug on the rear of the truck.
Or cut the blue wire at pin #2 C205 cab side and then run it to the rear.

C205 Images below:


Complete wiring:


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