I tried looking this one up because my nephew has this engine- but is several states away so I cannot just pull the shell and check.
https://www.lionelsupport.com/...el-LionChief-6-81677
As a note, the blue and orange wires would appear to be tied to direct power input- just the solder joints on the back of the board.
So- just trying to read between the lines- I think you are trying for directional lighting. and hoping that S2 provides that output?
I wish I had an answer but yes, I think testing with a meter or scope is about the best we could hope for since it's undocumented and unused.