I looked at the data sheet, I would suspect the hall effect sensors may be for the internal limit switches. I also suspect the red, black, and yellow wires are connected to an internal pot. You can check for a pot by measuring the resistance across the red and black wires to see if the resistance is something like 5k or 10k. If there is a resistance like this, then measure the resistance across the black and yellow wires as the actuator moves full stroke. If the resistance changes from ~0 to the resistance measured across the red and black wires, the actuator has an internal position pot (a good thing!). Below are the firgelli actuators with internal pots.