i also have a cat m50d. power steering won't come on at all. power steering only works while running hydo's lift tilt s/s. i talked with the cat dealer they said they thought the logic board turned on and off low speed pump for p/s. so i removed the logic board and sent to flight systems. supposedly rebuilt it got it back today installed same problem. anyone got any ideas. turn key on main power contacter closes. but no p/s pump. turn hand wheel still nothing. use hydo's and p/s works. please help.