Hi Michael,
For performance reasons the custom field weight is disabled for the regular engine. There are two possible options in this case:
1. Is to use the index table engine, however it is worth noting, that exact matching multiple keyword phrases (aka the whole field as one) is not possible, only separate whole words. This documentation can help you set up the index table, and then under the relevance options you will be able to change the custom field relevance to a much higher value.
2. To make a direct modification to the regular search file to enable custom field matching relevance. To do that, you will have to
– Open up the wp-content/plugins/ajax-search-pro/includes/classes/search/class-asp-search-cpt.php file on your server
– and replace it’s contents with this.
Please make sure to have a back-up of everything, before making direct changes. This change unlocks the custom field relevance query, and increases the result relevance, when a match is found within the choses custom fields. (chosen under the General Options -> Sources panel)