Hi,
Instead, I would create a fsm "BUS" likely on the gameobject root of this bus. and it would know the two brake lights gameobject ( two variables that you reference manually during editing time) and since this is in the same hierarchy, everything is cool, as a prefab I mean.
then it's easy to get their references at runtime, use GEt Fsm GameObject on the "BUS FSM" itself,
the other way is to create a global variable called "BREAK LIGHT ON" and "BREAK LIGHT OFF" and broadcast that global event JUST to the childs of the bus ( Send Event action can do that), and then you don't even care about the actual gameobjects themselves, you just create an fsm that receives these global event son the breaking light themselves and done.
bye,
Jean