My Horse Trailer Breakaway System Failed.
A trailer breakaway system is designed to bring the trailer to a safe stop should the trailer be disconnected from the tow vehicle while driving. For this to happen you must have operational electric brakes on the trailer. And the breakaway system must be operational.
The best way to test is to pull the pin and make sure the trailer wheels can’t move. Your horse trailer breakaway system is essentially an open circuit until the pin is pulled.