I tried using this plugin for custom taxonomy search. As mentioned by other people on the forum, the plugin did not work. After digging in the code, I fixed that issue.
I also needed to exclude a category from search and when I added Exclude Category, the search returned no results. Again, dug into the code and found a small problem. Fixed that issue as well.
I do not know how to contact authors and send them the corrected code. I can share the code if it can be of help to anyone.