I believe the 900 can be identified by only having the 5, 8, and in/out buttons. The later models have more features. Also, IIRC, the ones from the Eclipse A have an edge connector with far fewer pins. The B and C have more pins. Granted, I don't think the pinout is exactly the same. In addition, I recall a relay on board, probably 5V, which needs to have power for the thing to work. Otherwise jumper around it I guess. This is all from memory, so...