3 Node mongo db authentication setup fails
As shown in your question you are now connected with the secondary node. Since secondary may contain stale data, by default MongoDB won't allow you to read any data from secondary.
There are two options to read your data


Connect primary node (use the correct port number )
From secondary, run rs.slaveOk(). This will allow you to read data from the secondary.


Note: run rs.status() or rs.isMaster() to find out which one is primary.