***UPDATE **** Was still having issues with brakes locking loaded or unloaded at even low speed normal stop. Finally jacked the trailer up, took all 4 wheels off and was shocked at what I found. It appeared that at some point, the Previous Owner had forgotten to unhook the brake cable before driving off. The cable had been sheared and spliced back inside the coupler.
All 4 wheels had the leading pad almost metal to metal. The wheel cylinders were over extended. The actuator was shot. Replaced all 4 backing plates with new, new actuator and bled all lines several times over. Trailer stops like it should now, no more locking brakes.
What really shocked me was the amount of damage to the pads. The trailer was bought new, was pulled a distance of 70 miles and the boat was put in the water at a lake house. During the winter, the trailer was pulled a total of 2 miles each year to launch/retrieve the boat 1 time per year until I bought it.
Previous Owner stated that he had forgot the cable many years ago but didn't know he had done any damage other than shearing the cable. He told me this after I asked him about it.
$800 later and the trailer is safe and ready to tow again