multiple installs with one set of users

After hours of searching and pulling my hair out I finally figured out how to have my three WordPress installs share one set of users.

In wp-settings.php in your root WordPress directory of the install you want to get its users from a different install, change
$wpdb->users = $table_prefix . 'users';
to
$wpdb->users = 'databasename.wp_users';
where databasename is the name of your database (obviously enough) and wp_users is the user table you want all of your users stored in.

You really need to think about this before you do it. The two seperate installs I modified are very recent so there were only a few users to move (in phpMyAdmin) and only two comments to change the author id of. If you have alot of users and/or comments I would not suggest doing this (unless its to a new install).

I hope this was relatively clear, I’m pretty tired.