Western Star utilizes relay in master power distribution, they call PNDB. When this device is faulty it interrupts the power to engine causing truck engine to shut down. This shut down has happened with the truck fully loaded (71,000 LBS) traveling at 60 mph a couple of times. With no engine power you lose power steering. This is a very dangerous condition that I have discovered is more common than it should be. Talk to any Western Star service department. The Service Department knew exactly what the problem was and related to me this is common.