Genesis/Mega Drive, 4 way play schematic?

I'm quite sure I had a schematic for this not too long ago, but am having a fair bit of trouble locating one now...
If anyone has one, that would be great!

I am mostly interested in the EA Games version, although I know they aren't interchangable with all games, it appears that Street Racer can use the EA Games variety (plus I have a number of EA Games

Any help would be great! If I do find it, I'll post the schematic here, and follow up with pics of my build

Thanks!