EOS switch must be normally closed with tungsten contacts

System 3-7 EOS switches are normally closed: touching at rest and open 1/16" to 1/8" at full stroke. A mis-adjusted EOS burns the coil. Many later WPC games use normally open EOS switches with small gold contacts, which burn up here; use an EOS with large tungsten contacts as on pre-Fliptronics WPC games (before Addams Family). Needing to flip a WPC EOS over to make it normally closed is a sign it is the wrong one.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Most flipper faults are EOS switch faults
• Games with an upper flipper switch on the EOS stack
• Flippers dead after long storage: corroded button and EOS contacts
• Right flipper too weak for the top lock after a rebuild: lighter return spring

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)