Surge Brakes Locked Up

[ggray]

2007 22 Cruiser, 2007 MagicTilt trailer with Dexter UFP A-70 surge brakes.

Background, I have owned the boat and trailer for 4 plus years now, and have launched or retrieved the boat maybe 6 times on the middle to lower Chesapeake with somewhat salty water. Minimal rinsing afterwards. Unknown dunkings by POs previously, but last PO was on Pamlico, so not very salty at all. Anyway, last summer the brakes rusted locking both wheels, and needed both calipers replaced.

After that expensive repair, I was determined to rinse well after dunking. Which I did after the only retrieval last year, and drove a few (unneeded) miles with several stops to dry the brakes. So I'm dismayed that the brakes are locked up again, preventing the wheels from rolling forward or reverse. I am pulling on gravel now, and maybe a hard surface will force the wheels to turn.

I want to make sure I fully understand the braking system. I understand how surge brakes work, and am now using one of those magnet secured devices that prevent the tongue from "telescoping" and applying the brakes. What I want to find out is if there is any electrical part to this braking system. I don't think there is, but the wiring has an extra (a fifth) wire. I've never had a trailer with brakes before this one, and am trying to learn.

So that's my question to the group. The only other reason I can think of for the brakes being locked is that prior to my buying the magnet device, I tried to back the boat + trailer very slowly into the parking spot. However before reaching the spot, the brakes locked. I rolled forward a bit to uncouple from the trailer, but I wonder if the brakes remained locked for the last 4 plus months and now won't release.