Williams Electric Trains was a small manufacturer started by Jerry Williams during the early 70's, specializing in O gauge and standard gauge reproductions (later discontinued).  In 2007, Jerry Williams retired and sold his company to Bachmann, who continued the brand name as "Williams by Bachmann."  If your locomotive is labelled "Williams by Bachmann" then it is fairly new (no older than 2007), and you can look up old catalogs on-line to find more info.

I bought a used Williams F7 A unit that is missing the die cast pilot (painted black).  Is it possible to order this part?  It doesn't show up in the on-line list of available parts.