<?php
add_filter('wp_nav_menu_items', 'add_item_to_menu', 10, 2);
function add_item_to_menu($items, $args){
if($args->menu == 'principal'){ //Menu name.
$items .= '
<li>
<a href="http://localhost/contact">
<img src="http://localhost/uploads/contact.png">
</a>
</li>
';
}
return $items;
}
?>