All Post Types in Search

all_post_types.php

<?php

function ecpt_include_post_types_in_search($query) {
	if(is_search()) {
		$post_types = get_post_types(array('public' => true, 'exclude_from_search' => false), 'objects');
		$searchable_types = array();
		if($post_types) {
			foreach( $post_types as $type) {
				$searchable_types[] = $type->name;
			}
		}
		$query->set('post_type', $searchable_types);
	}
	return $query;
}
add_action('pre_get_posts', 'ecpt_include_post_types_in_search');

You should probably be checking $query->is_main_query().

Good call.