You'll have to do it like this:
function SelectDropDownValue(Service_Name, DefaultValue, Fieldname) {
var result;
switch (Service_Name) {
case "SUBDIVIDED":
case "ARB":
case "MINING CLAIM":
case "SECTIONAL":
case "MAPS AND SUBDIVISIONS":
if (DefaultValue == "N" && Fieldname == "BACKTOBASEORDEROPTION") {
result = "PLANT_BEGINNING";
}
else if (DefaultValue == "1") {
result = "MOST_RECENT";
}
else if (DefaultValue == "2") {
result = "SECOND_MOST";
}
else if(DefaultValue == "N" && Fieldname=="SORTINVESTIGATIVEOPTION" || Fieldname=="SORTORDEROPTION")
{
result ="Newest";
}
break;
default:
result = "";
break;
}
return result;
}
That way it should work. BTW I moved all of your breaks out from the else-ifs because I like that style better and in this case there really isn't a difference.
Happy coding!