This is probably considered necroposting, but I thought I'd add to this thread.

I found this topic through Google with the search terms "TurboGrafx 16 composite" and it's probably the only relevant link so I thought I'd chime in.

You can get some nice pre-made cables (with minimal modification) that can fit the pins on the expansion slot on the back of a TG16. I get them at http://www.frontx.com . They're located in Malaysia, but they're safe because I've bought from them before. Free international shipping too. Which is beyond nice.

They offer a lot of pre-made cables you can't get anywhere else as far as I've seen. Cables that include external to internal connectors and odd stuff like that which you usually only get OEM with new computers, add-in cards and motherboards.

Following this diagram: http://www.gamesx.com/misctech/pcebp.php I've worked out how to use a 1/8th inch stereo jack to a 1x3 pin header connector cable, re-jigger modifying the cable by pulling out the center ground pin (which is easy to do with these header blocks) and inserting it into a single pin header connector, then I simply use a 1/8th inch to stereo RCA adapter I had laying around (in truth having a 1/8th connector gives me more flexibility anyway). Then what I do is make my own RCA to a 1x2 header video cable by buying a strip of female terminals (which are nice to have extra of anyway) and a 1x2 header connector (marking which is ground and which is vid) and taking an existing RCA cable with one end stripped and tinned make my video connection.

Is this a good solution? Let me know. The way I look at it I've saved myself half the work by buying a pre-made cable that I only have to modify a little bit. In many ways it's similar to what this guy has done except with the use of a stereo jack and only one ground instead of a pair of stereo RCA plugs and two grounds. The video remains the same though except with a more stable 1x2 header since the vid and ground are located right next to each other.