Which component would be used to connect the thermostat wires?

The sub-base is integral to the installation of a thermostat because it serves as the mounting point and connection interface for the thermostat wires. When installing a thermostat, the sub-base helps organize and secure the wiring, making it easier to connect the wires coming from the HVAC system. This component effectively bridges the connection between the thermostat and the various wires that control the heating and cooling equipment.

While the circuit board may play a role in controlling the thermostat's functions and communication within a system, it does not specifically serve to connect the wires from the thermostat itself. The fuse box is responsible for electrical distribution and protection but does not directly connect the thermostat wires. A relay switch is involved in switching electrical circuits but is not designed for the direct connection of thermostat wiring. Thus, the sub-base is the most appropriate choice for connecting thermostat wires, ensuring a functional and safe setup.