My son has a 1989 Lincoln Town Car,and the rear brakes don't work..i need help !?

My son took his 1989 Lincoln Town Car down to get it smog checked,but he was told that they could'nt do the smog check because the rear brakes do not work at all.The front brakes work just fine.The repair manual does'nt say anything about why the rear brakes would not work,or where to even look for a problem.Can somebody please help me out here and give me a idea were i might begin to look,and how i might correct the problem.