What color wire was attached to each labeled terminal on the OLD thermostat?

If you didn't write down how the OLD termostat was wired, I'd recommend you find the wiring instructions for the brand and model of the HVAC unit to which you're connecting the new thermostat. Can you find the brand and model?

There appear to be five wires in the thermostat cable. This could be it:

• Blue - Common (C)
• Red - 24 volts (Rc)
• Yellow - AC (Y)
• Green - Fan (G)
• White - Heat (W)

Thanks for response, here goes picture below of the old Honeywell Thermostat wiring.

I also attach a clearer picture of the electric furnace wires. I see a unused blue wire on both ends

Im installing the Amazon Thermostat:

https://www.bestbuy.com/site/amazon-smart-programmable-thermostat-with-alexa-white/6483323.p?skuId=6483323

You are going to connect the wires to the corresponding connections on the new thermostat (G, W, Y, and Rc). You will need a C connection which you can be the unused blue wire. The challenge is figuring out where to pick up the common (ground connection). Does the red wire connect to the transformer in the photo? If it does then the other side wire to the transformer should be the common connection.

Will you be able to pull the blue wire (which will become the Common (C) wire) out of the wall so you can attach it to the new thermostat?