Even if somebody had a Williams manual, they are not much help.
Do you know when this Williams engine was made? Or what is on the box? Is it Williams, Williams Reproductions, Williams Crown edition or Williams by Bachmann?
These are the five most common on box names for Williams. The reason I mention what is on the box, is because there are at least three sound systems that could have came with a Williams, anything from just a basic horn, Station Sounds by QSI, to the True Blast 2 system. The True Blast 2 system now has at least two versions, one made for Williams before Bachmann, one made for Williams by Bachmann and a new polymorphic True Blast2 made by Williams by Bachmann.
Let me know what is on the box or engine and I can probally tell you what sound system is in a Williams, and how it works.
Lee Fritz