jQuery Grid Plugin - jqGrid

Hello - I am trying (desparately) to fill my edit form dropdown from a db call (LINQ specifically). I can't seem to get the format it likes because my dropdown always comes up empty. I know I'm hitting my controller code because I'm setting a break point in it and hitting it. As a test I am bypassing the db call and just passing back a string I think should work but is not . Please any suggestions much appreciated.  I could not find in the doc the format it is looking for. Here's my code:

Controller:       

public string GetTypes()
        {
          
            string strRet = "";

           
            return "1:Sideboom;2:Truck;3:Car";
           
        }

aspx:

    jQuery(document).ready(function() {
        jQuery("#sandgrid").jqGrid({
        url: '/EquipTrack/GridData/',
            editurl: '/EquipTrack/Edit/',
            datatype: 'json',
            mtype: 'GET',
            height: 255,
            width: 755,
            rowNum: 5000,
            colNames: ['ID', 'Type', 'Make', 'Model', 'Year', 'Location', 'Insp Due', 'Serv Due', 'Miles/Hrs', 'Milage Dt', 'Reg By', 'Mngd By', 'Tag Exp',''],
            colModel: [
                   { name: 'equip_id', index: 'equip_id', width: 65, editable: true },
                  {name: 'type_desc', index: 'type_desc', width: 130, editable: true, edittype: "select", formatter: 'select', editoptions: { dataUrl: '/EquipTrack/GetTypes'} },
                   { name: 'make_descr', index: 'make_descr', width: 80, editable: true },

.

.

.

       }).navGrid('#sandgridp',
     {}, //options
     {reloadAfterSubmit:false}, // edit options
     {reloadAfterSubmit:false}, // add options
     {reloadAfterSubmit:false}, // del options
     {} // search options
     );
         
        $('#sandgridp_center').remove();
        $('#sandgridp_right').remove();
    });