Ya, they are optically isolated solid state relays (SPST) used on Traflomatic & TAC50 controllers. The input modules are 24vdc or 120vac and switch 5 vdc to the CPU. The output modules have 5 vdc coils and switch contacts for either AC or DC. So I think it's just the 4 modules we would need it to test, if there are more I'm sure someone will correct me.

http://www.crouzet-ssr.com/english/products/_iom.shtml