nest thermostat

[just2]

have wires bk and b/c on old therm. where do they go on new them.

[EdmondB]

Hello just2, 

Thanks for posting here in the Community. Based on the terminal of the wires from your current thermostat, this is a proprietary system. This is not compatible with any type of Nest Thermostat. However, some proprietary systems can be rewired by a pro installer to be compatible. Check out this link for Nest thermostat compatibility.
 

Let me know if you have additional questions.
 

Best,
Edmond