Which WPC schematic manual covers the backbox boards
Games up to Gilligan's Island often print the backbox board schematics in the game manual. Later games need the separate schematic book: 16-9473 for pre-DCS WPC-89 games (Funhouse to Twilight Zone), 16-9834.2 for DCS and WPC-S games (Indiana Jones to Jackbot), and 16-10159.2 for WPC-95 (Congo to the end).
Systems
Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part One, Clay Harrell (pinrepair.com)