From SBIG's site:
RELAY ADAPTER BOX is used with older telescopes that do not support the Models ST-5C, ST-237, ST-7, ST-8, ST-9 or PixCel 255 and 237's digital interface. This unit provides four SPDT relays (like the Model ST-4 interface) and offers complete isolation of the camera from the hand controller electronics.
I never did use it! Comes with lots of cables!
Price: $47 and I'll pay shipping within the lower 48.