I have opposite question how to use simple select for extra custom fields ?)
The code in searh.php
<div class="sidebar-hooks">
<?php
GLOBAL $search_hooks;
ob_start(); // SAVE HTML
if(osc_search_category_id()) {
osc_run_hook('search_form', osc_search_category_id());
} else {
osc_run_hook('search_form');
}
//echo $search_hooks;
$search_hooks = ob_get_contents(); // CAPTURE HTML OF SIDEBAR HOOKS FOR FOOTER (MOBILE VIEW)
?>
</div>