In one switch position the two primary windings are in parallel for 115VAC, and other position series for 230VAC (apparently red is one prImary and black the other).
It is important that the polarity of these windings agree or they will fight/cancel each other.
There may be a dot on the body of the transformer by the positive lead of each winding (positive is a polarity/phase thing not a voltage thing).
JR