There are a couple possibilities. One is that you burned the ground lead somewhere in the printed circuit. This is usually pretty evident if you open it up and examine the ground trace.
Another possibility is that in disassembling the cluster you haven't re-established the link across the various units. They are connected by contact as they are screwed together. I have seen a number of cases where just retightening the screws on the back will make the connection.
Bosch Master, ASE Master, L1
33 years MB technician