I have a maintence light ON in my 89 mighty max 2.6L 5 speed. The truck has 124,000 miles on it. I dont know what the previous owner hasn't done or has done so I am in the dark as well. How can I check what it needs? or what do I need to do to it? I have changed the oil and filter, fuel filter, and flushed the coolant system and put new coolant in. The truck drives good and running smooth in idle.