Brake Controller acting weird - video included

[Aubiexx]

I have a 69 overlander. I have found that the brake controller to be odd about working properly and am trying to find out if the problem is the controller or on my trailer.

Sometimes it will work perfect, and I have found that 4.5 is about the right setting. Please see below as to what is going on.

I also at times will turn the setting to the most friction, which should be 10.0, but often doesn't go above 1.5 when in the same position.

Thanks in advance for your help diagnosing this.

Trailer brake - YouTube