Well, this is fun; the schematic is all chopped up, but you can find it and the manual here: http://mirror2.ipdb.org/files/2352/Williams_1974_Star_Pool_Maunal_Supplement_Schematic_Diagrams.pdf
Check the NO sw. 'D' (last one away from coil) on the Lock relay, the Game Over relay, and the wiper finger on the Ball Count unit for cleanliness and contact.