This isn't really a guide, but maybe interesting to people who like fighting games.
I have many of these nice 6-button Genesis pads lying about, yet absolutely no good PS2 pads and only one fight stick. I took a PS1 digital pad, cut down the board a bit, relocated a capacitor and the wires to all be on one side, and crammed it inside the genesis controller and made the necessary connections to the genesis pad’s buttons to allow me to use it with the PS2. Here are pictures as usual!