Installing Honeywell Wifi on Ruud Furnace with G wire replacement
Check your voltage from R to C terminals on the board to make sure you have 24 volts there. If you don't mind the feel of air moving, you would be better off just putting a short jumper from R to G. This will energize the fan relay to keep it running continuously and the best for you for constant air filtration and if equiped with a power humidifier will maintain the house humidity properly. Then using the G wire as proposed should work. Before you did this, did the fan start when flipping the fan swich on the thermostat to on for continuous fan operation? If you never tried it, it might be a good idea to change things back and do so to eliminate the chance that there's a break in the green wire. Or if your new thermostat is in place, leave the power off change things back on the Furnace and disconnect the red for power and the green and just hold them together with the power back on for a few seconds at the thermostat to see if the fan starts, again to verify no breaks in the green wire.