This is your Heater Control Valve
But I am going to explain what it does.
First of all the "wire" you see is actually a vacuum line, it's a hollow (hopefully) air-tight tube that passes vacuum to the Heater Control Valve.
The heater control valve is a vacuum actuated valve that in the open position allows fluid to pass through and in the closed position does not allow coolant to pass through. This valve is normally open, meaning that when there is no vacuum present the valve will allow coolant to pass.
On your HVAC controls your options should be [Max A/C, AC, Vent, Vent/Floor, Floor, Defrost+Floor, Defrost only]. When you have the controls set to "off" or "AC" this valve closes to prevent coolant from entering the heater core. In any other setting (I believe, there might be another though) this valve is opened and allows coolant to circulate through the heater core.
This is to maximize AC efficiency because when your heater core is full of (hopefully) 192F coolant you are going to be fighting that to produce cold air. It also closes off this area of the coolant system which increases your coolant system's efficiency as a whole (not having to circulate through an area that doesn't really provide any cooling aside from the heat you draw away into the cabin).
This isn't something you will find on every vehicle as it isn't truly necessary. Lots of vehicles simply allow coolant into the heater core 100% of the time.
This means that it can be bypassed as a quick fix if you really need to and don't have immediate access to parts, just connect the lines. Although you probably won't have connectors for the lines either if you can't get access to such an easy to find part ;P