somewhere the wire that was used is damaged or not connected properly. If you are able to test the continuity of the wires from one vac head to the other that would be able to tell you where the damage is. There should be two wires at each head except for the last one in the run which will have one. The wire that was used is phone wire. Thats ok for this but if two colors of wire dont work , try the other two on all the vac heads. Maybe just one of the wires used is damaged and not all of them. Make sure all vac heads have the same to color wires used. Try different combinations of colors at the vac heads . Also at the vac unit be sure to change the colors there too.