The wheels are NOT locked with the trailer disconnected.

The wheels are free to roll forward and backward unless there is pressure applied to the tongue pushing back on the trailer. To prevent this from keeping you from being able to back up there is an electronic bypass that activates when you place your vehicle in reverse. The electric signal to the trailer reverse lights activates this solenoid bypass the brakes allowing you to back up without the breaks engaging. If you take away this electric signal the wheels will be free to roll forward or backward unless pressure it applied to the tongue.