The C-connection you can find in alternators from car brands like Toyota and Honda. Mostly you can recognize the c-connection by the square and oval shape plug.
The connection definitions are as follows:
L = Lamp
IG = Ignition
C = Computer
FR = Feedback
The C-connection may seem hard to test, but this is definitely not the case. Just connect the c-terminal to ground and you will notice that the VSP drops to 12.8 Volts. For example during acceleration of the car the terminal is connected to ground by the ECU and the alternator is temporarily disabled. This is fuel saving