I am replacing an old 3-wire thermostat with a Honeywell programmable thermostat. It will be connected to an old oil-fired burner (no AC). The red and white wires are easy to figure out, but there is a green wire that had become disconnected, so I don't know where it was connected originally. The Honeywell instructions say to connect the green to the 'G' terminal (fan relay), but I don't know if that applies to me. My heating system has six zones, each controlled by a separate thermostat. Any advice would be greatly appreciated.