There is an output lead "CA" from each 400 card that sends interrupted local generator, through a relay contact, to the ring side (slate/yellow) of the ringer pair to the phones. If you loop the CA from line 1, line 2, line 3, etc, so that whenever any one, or more, of those cards detects ringing from the CO line, it will send local generator into the CA bus.
CA = "Common Audible" The CA leads, one per line card, appear along the side of the 66 block in the shoebox. They provide the hot side. You must also provide a RG (Ring Ground) on the yellow/slate wire to each ringer. These can be left multipled, as originally designed. You are just going to open the hot sides individually.
I suggest that you put a break contact of the Sandman device in series with the individual CA lead from the 400 card associated with the incoming CO line. You will not be interfering with all the CA leads, which would normally be strapped together. You will only be opening the wire that runs from the 400 card's CA output to the common bus. You could do this 4 times, with each relay opening an individual CA lead.
Clear?
