Can only get one of two custom menus to display

Question

I'm a wordpress beginner and at the moment struggling to get to grips with custom menus. I have created two menus. Wordpress tells me the theme supports two menus. I have

<?php wp_nav_menu('menu=services_menu'); ?>

Where I want one menu to appear. I have

<?php wp_nav_menu('menu=left_navigation'); ?>

Where I want the other menu to appear.

I have

<?php
if ( function_exists( 'register_nav_menus' ) ) {
    register_nav_menus(
        array(
          'services_menu' => 'Services menu',
          'left_navigation' => 'Left vertical navigation Menu'
        )
    );
}
?>

In functions.php.

Both menus appear under "Appearance -> menus ->Theme locations" and are associated correctly. But only the services menu ever appears, in both locations. I've read a welter of different solutions to doing this, none of which seem to have any result other than the one described above. Where am I going wrong?

Answer 1

The problem is that wp_nav_menu() should really only ever be calling theme_location, not menu.

The Theme defines menu locations, and then places those menu locations in the template. The user defines menus, and assigns menus to theme locations.

So, change this:

<?php wp_nav_menu('menu=services_menu'); ?>

...to this:

<?php wp_nav_menu( 'theme_location=services_menu' ); ?>

Answer 2

<?php wp_nav_menu( array('menu' => 'menu name' )); ?>

possibly?