Steering is actuated by the accelarator pedal. Have you got any fault lights flashing on either of the curtis control units. Have you got DC drive and DC lift, AC drive and DC lift or AC drive and AC lift. I f you have got DC drive and DC lift. Pin no. 10 on the drive controller feeds pin 10 on the Lift controller once the accelarator has been pressed. This will bring the pump motor in at a reduced speed for the steering.

You can also check the fault codes/history by plugging in a curtis programmer.