template_preprocess_search_results variables not seen in search-results.tpl.php

I'm trying to create a variable in template.php. I define the variable in _preprocess_search_results. I try to use the variable in a local copy in my theme folder of the file search-results.module.php. The variable isn't being seen there. My theme is earthen. When I use the zen theme everything works great.

How can I debug this?

Thanks very much.