You cannot properly activate your trailer brakes
without a correctly wired & set up brake controller. If you apply power to the electric brakes of your Boler
without using a controller the brakes will simply 'lock up' or at least apply maximum braking power they're capable of, continuously until the power is interrupted, you blow a fuse, or a wire gets too hot.
There are several good brake controllers at reasonable prices. I personally prefer the Tekonsha Prodigy series (Prodigy, P-2, or P-3). Not sure if your Ranger is already 'wired' for a brake controller. If it has a factory tow package chances are it is already wired for a brake controller. If not, it is a relatively simple matter to trace the necessary circuits & connect to them. If your truck is already wired for a controller, when you order the controller you can probably order a 'pigtail' made especially to connect your vehicle to the controller you select.