Final answer:
The red connector in a set of RCA cables is generally used for the right channel audio and should be plugged into the corresponding red port for audio input or audio output.
Step-by-step explanation:
The red connector in a set of RCA cables is typically used for the right channel audio and should be plugged into the right channel audio input or audio output port, depending on whether the source is sending out sound (output) or the device is receiving sound (input). RCA cables are color-coded: red and white (or black) for right and left channel audio, respectively, and yellow for composite video. If you're connecting a home theater or stereo system, make sure the red RCA connector goes into the red port for the right audio channel on both the source and the receiving device.