64 Dart cluster connector

I assume you had the battery disconnected when you started this project?
As old as that board is, it's possible by moving it around some of the connections or pins connected to the board cracked loose. Happened to me with my '66. Get a ohmmeter to check continuity of the connectors to the tracers. Clean the big round connector with electrical contact cleaner and make sure that the connections are not too loose to the respective pins when you plug it back in (you may need to squeeze them a hair with pliers). Believe me ... it is a very finicky component.