In the map include file find any line that starts:
marker.openInfoWindowHtml
and comment it out:
//marker.openInfoWindowHtml
To find the map include file, look at the code on your page before the </head> tag, for PHP, there will be a line similar to:
<?php include("google_javascript/wagmp_map_1.php"); ?>
The google_javascript/wagmp_map_1.php is the page to edit.