No worries
May I suggest to give it a test first. Just wire it direct to battery before installation.
Connect 12V power wire(Black) to battery positive + earth wire(White) to battery negative + 12v power to brake switch wire(Red) & test power coming out of the brake wire(Blue).
The brake wire(Blue) will output 0-12V, depending on position of output slide, when Brake switch wire(Red) is connected to positive battery & no power on brake wire(Blue) when brake switch wire(Red) is disconnected.
FYI: Electric Trailer Brake Controllers supply a variable voltage from the truck, from 0 to 12 volts, to the trailer brakes. More voltage, greater stopping power. The brake controller varies the voltage to the trailer to allow for brake modulation. Without the controller, the brakes would get full 12 volts and the trailer tires would lock up, every time.