Try this for a complete site wide redirect to HTTPS://     
RewriteEngine On    
RewriteCond %{HTTPS} off    
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]    
All older pages should be caught under this rule.     
Also remember to update your Search Console profiles, sitemap etc
Update any hard-coded links or blocking rules you might have in your robots.txt that might still be pointing to HTTP directories or files.