After a few hours of experimenting, including installing the latest version, I found the following lets me automate my logon to VM/CMS. Replace the strings myuserid and mypassword with yours. The \t tabs to the password field and the \n performs the ENTER.
"C:\Program Files (x86)\wc3270\wc3270.exe" -loginmacro myuserid\tmypassword\n +S