Actually, that didn't work. And here's why:
The
[[!simpleSearch]] call on the results page also needs
&searchIndex=`whatever-the-search-index-is`, but this:
[[!simpleSearch? &searchIndex=`[[+searchIndex]]`]]
did not work (I tried cached and uncached searchIndex).
So I had to create a snippet that pulls the $_GET variable from the URL and put that snippet in the simpleSearch call.
Here's what I did:
FORM
<form id="sisea-form-[[+searchIndex]]" ...
simpleSearchForm Call 1
[[!simpleSearchForm? ... &searchIndex=`search1`]]
simpleSearchForm Call 2
[[!simpleSearchForm? ... &searchIndex=`search2`]]
simpleSearch Call (for search results)
[[!simpleSearch? ... &searchIndex=`[[!getSearchIndex]]`]]
getSearchIndex Snippet
<?php
foreach($_GET as $k => $v){
if($k == "search1") return "search1";
if($k == "search2") return "search2";
}
Hope that helps!