Adding a c-wire to a mastertrol system.?

I have a mastertrol HVAC system. I would like to install a new thermostat with wifi abilities. There is no c- wire. Each zone thermostat has extra wires in the bundle. Can I connect an extra wire from the each of the 3 thermostat bundles to the c terminal as seen on the bottom left of the diagram to act as a c-... show more I have a mastertrol HVAC system. I would like to install a new thermostat with wifi abilities. There is no c- wire. Each zone thermostat has extra wires in the bundle. Can I connect an extra wire from the each of the 3 thermostat bundles to the c terminal as seen on the bottom left of the diagram to act as a c- wire? If not, can I get a c-wire plug in adapter in the basement to power all 3 zone thermostats by connecting an unused wire to it and then the c terminal on the thermostat? I just don't want to have an adapter plugged into the wall and connected to each of the three thermostats if I don't have to.
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