Hi RL_Sql,, at this moment you have installed a default instance in passive node , it was installed in the first Sql cluster setup...
The default instance of the SQL Server 2000 database engine operates the same way as the database engines in earlier versions of SQL Server. The default instance is identified solely by the name of the computer on which the instance is running, it does not have a separate instance name. When applications specify only the computer name in their requests to connect to SQL Server, the SQL Server client components attempt to connect to the default instance of the database engine on that computer. This preserves compatibility with existing SQL Server applications.
There can only be one default instance on any computer, the default instance can be any version of SQL Server.
Multiple Instances of SQL Server on a Failover Cluster
You can run only one instance of SQL Server on each virtual server of a SQL Server failover cluster, although you can install up to 16 virtual servers on a failover cluster. The instance can be either a default instance or a named instance. The virtual server looks like a single computer to applications connecting to that instance of SQL Server. When applications connect to the virtual server, they use the same convention as when connecting to any instance of SQL Server; they specify the virtual server name of the cluster and the optional instance name (only needed for named instances): virtualservername\instancename. For more information about clustering, see Failover Clustering Architecture.