Looking for logging into the Joomla Super User Error 503 site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Joomla Super User Error 503 site. After that you can login as usual with your login credentials.
https://joomla.stackexchange.com/questions/19276/other-joomla-user-login-works-fine-but-admin-user-cant-login-503-shown
https://forum.joomla.de/thread/4510-http-error-500-joomla-administrator-login/
https://forum.joomla.org/viewtopic.php?t=911625
https://www.joomlapolis.com/forum/153-professional-member-support/222004-solved-503-server-error-accessing-configuration-backend
https://stackoverflow.com/questions/51634010/error-503-when-logging-into-joomla-backend
https://www.daniel-net.de/index.php/gedankenablage-blog/it-technik/3-strato-und-joomla-error-503
https://www.joomla.ch/forum/138-allgemein/36198-backend-login-fehler-500
https://serverfault.com/questions/709912/503-error-when-trying-to-login-joomla-3-3-1
http://www.joomlaportal.de/joomla-2-5-allgemeine-fragen/296721-administrator-login-geht-nicht-http-fehler-500-a.html
https://github.com/joomla/joomla-cms/issues/18047
https://sucuri.net/guides/how-to-clean-hacked-joomla
https://www.collectiveray.com/joomla/joomla-tutorials/joomla-blank-page.html
https://rockettheme.com/forum/general-discussion/231470-solved-joomla-2-5-blank-administrator-backend-after-login