//Show Product Search in Header function new_nav_menu_items($items, $args) { $my_product_search = get_product_search_form( $echo ); if($args->theme_location == 'main_navigation'){ $items = $items . $my_product_search; } return $items; } add_filter('wp_nav_menu_items', 'new_nav_menu_items', 10, 2);