So Ive been trying to install a new Honeywell wi-fi thermostat. I have been unsuccessful in any event. I have a third wire unused at every thermostat in my home which is black. This black wire tuns back to my Honeywell relay R8888A/B.I do not know how to get power from the relay board and have spent numerous hours trying to rewire the black wire to get 24vac to it. If someone could please help me out!! Thanks
Connect your thermostat's C wire to the C terminal labed XFMR C. This worked for me using an Emerson Sensi Thermostat. Using an AC volt meter you can measure 24 volts from the thermostat RH wire and the transformer C terminal during a call for heat. This will provide power to the thermostat at all times.