For terminals that are connected to /dev/term/a or /dev/term/b serial ports on a system, predefined services are provided.
See Using Your Assigned Administrative Rights in Securing Users and Processes in Oracle Solaris 11.4.
For example, to enable login services for /dev/term/a:
# svcadm enable svc:/system/console-login:terma
# svcs svc:/system/console-login:terma
The output should show that the service is online. If the service is in maintenance mode, consult the service's log file for further details.