to make it work I did this

it seemed to not load the script on the page when needed, so I’ve simply hacked it and now it loads on every page (I’ll figure out a better method eveuntually), tp do this I commented out lines 46 and 50 of chosen.php, so it looks like this:

//if ( self::contains_select() && ! is_admin() ) {
			wp_enqueue_style(  'chosen', self::$chosen_url . '/chosen.css' );
			wp_enqueue_script( 'chosen', self::$chosen_url . '/chosen.jquery.min.js', array( 'jquery' ), false, true );
			wp_enqueue_script( 'wp-chosen', self::$wp_chosen_url . '/wp-chosen.js', array( 'chosen', 'jquery' ), false, true );
		//}

the self::contains_select() part doesn’t seem to work.

Also, I used jQuery(document).ready(function($) { $(".chzn-select").chosen();}); in wp-chosen.js so that I can target my select boxes like this

<select multiple="multiple" name="cars" class="chzn-select">
  <option value="volvo">Volvo</option>
  <option value="saab">Saab</option>
  <option value="opel">Opel</option>
  <option value="audi">Audi</option>
</select>

hope that helps someone…

https://wordpress.org/plugins/chosen/