customer has and 1984 mastertrol mark v mabs-V-3 zone control panel that was working fine till he replaced the t stats with a LUX2900 programmable (3 t stats )3 zone , and they have 3 wires, I don`t think you can make the new programmable t stat work in place of the old round Honeywell (57?) any ideas , thanks, tom gray grayequuipment hvac services , grayequipment@yahoo.com ps only 3 wires in the wall, If there were 4 wires I think I could make it work,65 yr old tech