see note below -----8 7-----no connection
6---------chroma out
audio out -----3 1----- luminance (B & W signal)
audio in -----5 4----- composite video out
2----- ground
Here is the A/V connector of the C64 and C128 shown facing the rear of the computer. Note that early versions of the C64 have a 5 pin DIN connector while later versions have an 8 pin. The two are wired exactly the same, except that the 8 pin connector has a separated chroma (color) output on pin 6. Earlier C64s didnt have separated chroma. Note the U shape of the connector pins. Its different than the circular pattern of the RGB DIN connector on the 1902A monitor, for example. Note: the early two wire cable (5 pin DIN) is used for composite video and audio only, and a three wire cable (8 pin DIN) is needed for Y/C video and audio.
Important note: the later C64C and the C128 both have a power supply line going to one of the unused pins: pin 8. Be careful!!!