NH 5040, the 4wd light doesn't come on so not sure if 4wd is working, how do I tell, never needed to use islt as hay making tractor. Mechanical lever in cab so have jacked up front end and turn front wheel by hand turns easy enough other front wheel turns at same time opposite way assume because of differential, then put tractor in gear and engage 4wd lever but makes no difference can still turn front wheels by hand, so how do I tell if 4wd working?