hook_services_resource is not working
You can try:

/**
 * Implements hook_services_resources
 */
function test_module_services_resources() {

  $resources = array();

  $resources['search_results'] = array(
    'index' =&gt; array(
    'callback' =&gt; 'test_module_search_service_results_index',
    'file' =&gt; array(
      'type' =&gt; 'inc',
      'module' =&gt; 'test_module',
      'name' =&gt; 'resources/search_results.resource'
    ),
    'access arguments' =&gt; array('access content'),
    'args' =&gt; array(),
    ),
  );

  return $resources;

}


Ensure the resource callback test_module_search_service_results_index is located in your module subfolder

test_module/resources/search_results.resource.inc


Then try hitting http://www.example.com/api/search_results (using your site services endpoint)