To force https for a site (even if https is already defined in a site or URL setting within an application on the site, such as Wordpress), insert this code into a .htaccess under the /public_html of the site for which forcing https is desired:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
This will rewrite any inbound, non-https requests to their https equivalent.