Question from user mbucks334 at hvacadvice at reddit.com.

Answer:

The first photo is the wiring setup when it was working perfectly fine. I tried to install a different thermostat and couldnt get it to power on. I was going to just give up and try tomorrow and replace my old one in the meantime. Put it back on and wired it exactly how it looked before (minus the wire length exposure which I have since trimmed) and it wont work. This is connected to a furnace which I can hear go on – off when I switch it. The thermostat clicks as well but doesnt seem to send a signal to the furnace. What did I do wrong? All breakers are 100% for sure back on.

Answer from user mbucks334 at hvacadvice at reddit.com.

thermostat not working after disconnecting reconnecting wires