Dave, have you had the wheels of of your trailer to check the brakes?
I just sold my 13" Scamp
with brakes last month. My controller for it was one that I bought at Pep Boys about 8 or 9 years ago. It has kicked around my garage until last year when I installed it in my new P.U..
I just did a complete brake job on the Trillium
4500 that I just bought and the $45.00, 8 year old Pep Boys controller work just as well on the Trillium
as it did on the Scamp
It sounds to me like you have a problem other than your controller.
When I picked up the Trillium
the brakes were not working. I checked and the wires at the wheels were disconected. So I drove home with no brakes thinking I would have an easy job. The wiring was incorrect, one magnet was missing and there was at least 3 pounds of grease in each brake drum. The moral of the story is if you have not had the wheels off, do it and save yourself some possibe future problems and pack the wheel bearings while you have them off.