i have a client that wants to build the exact same monitoring panel that was built in the early 70's and it uses a Sigma Datacel Optical Relay. Part number is 301R2-150. This part is now discontinued and i was trying to figure out how to cross reference to something else. Does anyone have any ideas? Pin 6 is connected to 120VAC (N) and pin 7 is connected to 120VAC (H). Pins 1&2 are connected to one LDR and pins 3&4 are connected to a second LDR.