This article on WP Beginner covering how to add custom post type selections into an advanced search form. Fearless Flyer writes an article covering searching a custom post type with specific taxonomy terms applied to it via dropdown menu selects. A full on thread on WordPress Stack Exchange covering advanced search across multiple post types Full Article…
This is bullet proof down to IE7- Yea! As used by WooThemes for their great work – check out this JS Fiddle. Just use this css:
Firstly declare the variable: (customcategory) Secondly the array for adding the post: and finally create the dropdrown from the get_post_types function: Taken from WordPress Stack Exchange.