It seems to be a common change in 68 Classifieds to want a category to be pre-selected when visiting the search form. This way all the extra fields are already loaded by default. This short template hack will show how it can be done.
Please keep in mind that with this change you can only have one category selected and it is recommended that all your categories share the same extra fields.
Here is a screen shot with an example:

#1. Open search.tpl and find the following code:
$(document).ready(function() {
#2. Just below it add:
selectedCat(1); //where 1 is the category pre selected.
function selectedCat(type){
$("#response").show()
$.ajax({
url: 'ajax.php',
data: 'action=extra_listing_fields&do=search§ion=' + type,
type: 'post',
success: function (msg) {
$("#response").html(msg);
}
});
}
This also only works with v4.1.x because of the change in JavaScript library.
