[JRTJH]

This is strictly a hypothetical cause, but have you considered that as they were moving your trailer around the lot, something hung on the breakaway cable, pulled the pin and THEY (not you) melted the breakaway switch, wiring and magnets????? Seems to me it would be difficult/next to impossible for someone (you) familiar with the way a trailer tows, to not feel the brakes dragging as they pulled it into the service department for warranty repairs.

I'd think it's likely (not 100% sure) to be a problem they caused rather than one you caused. As said, if the brakes burned up, it should be a warranty issue or a dealer caused issue, but the problem then becomes: How the heck do you prove it ?????