AJAX callback fails using form_alter on two fields I have content type with two text fields field1, field2
so i'm using hook_form_alter() to alter my form and i'm added for the first field

autocomplete_path path

ajax callback and wrraper


and for the second field i'm added

prefix : with id ind the wrraper of first field

suffix


I want to add a AJAX callback to check the value of a first field and added this value to check a value of second with autocomplete .
The code:
function ajax_callback($form,$form_state) {         
        return $form['field_annonceur']['und']['0']['value'];
    }

    function newsletter_form_alter(&amp;$form, &amp;$form_state, $form_id) {
        //dpm($form['field_annonceur']['und']['0']['value']);
        if ($form_id == 'newsletter_node_form') {
            $form['field_annonceur']['und']['0']['value']['#autocomplete_path'] = 'admin/get_path/autocomplete_field1';
            $form['field_annonceur']['und']['0']['value']['#ajax'] = array(
                'callback' =&gt; 'ajax_callback',
                'wrapper' =&gt; 'autocomplete_id',
            );

            $form['field_campagne']['und']['0']['value']['#disabled'] = TRUE;
            $form['field_campagne']['und']['0']['value']['#prefix'] = '&lt;div id=&quot;autocomplete_id&quot;&gt;';
            $form['field_campagne']['und']['0']['value']['#suffix'] = '&lt;/div&gt;';

            if (isset($form_state['values']['field_annonceur']['und']['0']['value'])) {
                ['field_campagne']['und']['0']['value']['#disabled'] = FALSE;
                ['field_campagne']['und']['0']['value']['#autocomplete_path'] = &quot;admin/publicite/autocomplete_field2/{$form_state['values']['field_annonceur']['und']['0']['value']}&quot;;
            }           
            return $form;
        }
    }

autocomplete_field1($value_field1){};
autocomplete_field2($value_field1,$value_field2){};

but i get the same field  when i select a first field , the second field is hidden !!
before input on field 1

after input on field 1

What am I missing? Thanks in advance!
the solution is to return the target field in the ajax callback
so the code is :

function ajax_callback($form,$form_state) {         
        return $form['field_campagne']['und']['0']['value'];
    }