There is no Si auto, the only Si auto that was made between 92 and 2000 is the del sol Si, and it was an option. And no, the cluster for a del sol is not the same. The EX (positive, I have one in my garage that I took out of the car) and dx (fairly sure) had tachs.
Back to the point, did you plug all of the plugs into the back? Have you reset the ecu? Does the old one still work, and have you tried it to see if that still works correctly? Have you taken a look at the actual sockets for the plugs to see if there is any difference? You're not really giving much info here...