![Old Honeywell 2 wire AC thermostat (with 1 extra wire behind) - can I modernize this with Ecobee? : r/ecobee Old Honeywell 2 wire AC thermostat (with 1 extra wire behind) - can I modernize this with Ecobee? : r/ecobee](https://i.redd.it/i-need-to-install-a-c-common-wire-adaptor-so-i-can-use-a-v0-7oxbt2dnacta1.jpg?width=1600&format=pjpg&auto=webp&s=13e063e39ca893faecae4a5a860f610c3232e282)
Old Honeywell 2 wire AC thermostat (with 1 extra wire behind) - can I modernize this with Ecobee? : r/ecobee
![Honeywell Home C-Wire Adapter for Honeywell home Wi-Fi Thermostats and RedLINK® 8000 Series thermostats THP9045A1098 - Amazon.com Honeywell Home C-Wire Adapter for Honeywell home Wi-Fi Thermostats and RedLINK® 8000 Series thermostats THP9045A1098 - Amazon.com](https://m.media-amazon.com/images/I/71AjSMTbLJL._AC_UF350,350_QL80_.jpg)
Honeywell Home C-Wire Adapter for Honeywell home Wi-Fi Thermostats and RedLINK® 8000 Series thermostats THP9045A1098 - Amazon.com
![Xwartre UL Certified Thermostat C Wire 24V Transformer, White Adapter Compatible with Honeywell, Nest, Emerson, Ecobee, Wyze Thermostat and Most Doorbells (26FT Power Cable) - Amazon.com Xwartre UL Certified Thermostat C Wire 24V Transformer, White Adapter Compatible with Honeywell, Nest, Emerson, Ecobee, Wyze Thermostat and Most Doorbells (26FT Power Cable) - Amazon.com](https://m.media-amazon.com/images/I/51EPruGRJwL.jpg)
Xwartre UL Certified Thermostat C Wire 24V Transformer, White Adapter Compatible with Honeywell, Nest, Emerson, Ecobee, Wyze Thermostat and Most Doorbells (26FT Power Cable) - Amazon.com
![Old thermostat works, but I can't get the Honeywell T9 to work. T9 require C Wire that was not in the wall. I added C wire & RC wire via plug-in 120v Old thermostat works, but I can't get the Honeywell T9 to work. T9 require C Wire that was not in the wall. I added C wire & RC wire via plug-in 120v](https://i.redd.it/qgn9tccrp6a91.jpg)
Old thermostat works, but I can't get the Honeywell T9 to work. T9 require C Wire that was not in the wall. I added C wire & RC wire via plug-in 120v
![Trying to figure out which is the C wire to use for my new Honeywell Wifi Thermostat? - Home Improvement Stack Exchange Trying to figure out which is the C wire to use for my new Honeywell Wifi Thermostat? - Home Improvement Stack Exchange](https://i.stack.imgur.com/zrBB7.jpg)