I have encountered an unusual issue where the behavior is different
between FreeBSD 4.6 and 5.3. If I login and then su to root
successfully, then do a su to a non-root user I get:

pam_login_access: pam_sm_acct_mgmt: user-id is not allowed to log in
on /dev/ttyv0

In chasing this down it appears that the restriction is coming from
login.access which does have a limitation to prevent the non-root user
from logging in. Only members of the wheel group are permitted to
login. That restriction is essential to this system. However, I don't
understand why su is concerned about that. I need su to switch me to
that user. I suspect this may be controlled by PAM but haven't been
able to figure out just where that would be. How can I make su work
like it does in 4.6?