YourTheme_links doesn't work on sub theme
I believe it is a typo, the function should be MYTHEME_link and not MYTHEME_links.Possible other ways to identify is use theme engine phptemplate_link instead of your theme name.

Try clearing your theme registry. Also Check whether you have spelled your theme machine name correctly. 

function MYTHEME_link($variables) {
    print_r($variables);
    die;
}