Power Steering

My problem started as having heavy resistance when turning left at low speeds/at a stop and normal operation when turning left. I had a mechanic replace the gear box, pump, high pressure line, and install a filter just in case there was anything left floating around. Everything worked great for 3 weeks, then complete power steering failure. Took it back he replaced the pump and the gearbox again. 3 days later complete loss of power steering again. He recommended replacing the ball joints just in case, as that was the only thing he could think of, even though the suspension system checked out okay. During his test drive after replacing ball joints, and the pump and gearbox again, the power steering failed. The power steering system has no electrical connections to the pump or the gearbox. Any ideas?