Since this is the 2nd instance, we should select "Add to Existing Deployment?". Then we should key in the "Server URL" - which points to the 1st OpenAM instance.
Once the Server URL is entered, the LDAP Server will be auto-populated. Strange thing is the Port is populated with "null".
So is this going to work or not? I went ahead to continue with the installation.
The installation completed without any error! After installation, I logged into OpenAM Admin Console to double check. Everything is good. The LDAP port for my 2nd instance is reflected as "1389" - which is correct.
It's still a mystery why "null" was displayed in the installation wizard.