Hydraulic trailer brake problem

I've carried a spare controller in my truck's toolbox ever since I bought my trailer, just in case any funkiness ever occurred...never had to use it. The main reason is that I ran into an ol' timer first thing after buying my truck & trailer, that told me to wire in a brake magnet, somewhere...anywhere...in line...he said it(the magnet)offers the resistance the factory controller is looking for...Guess the magnet could of gone bad...tho, I don't see how...it just hangs on a wall in my basement. Still wouldn't explain what happen on the Wildcat trip...being as, I feel that is where the problem occured...