redmine_qbo/assets/javascripts/application.js

$(function() {
  $("input#issue_customer").autocomplete({ 
    source: function (request, response) {
      $.ajax({ 
        url:  "/filter_vehicles_by_customer", 
        type: "GET", 
        data: { 
          selected_customer: $("input#issue_customer").val();
        } 
      });
    });
  });
});