To add a bit to this:
black wires generally signify ground, red +5V and yellow +12V. You should be able to see on the board that the power traces mainly center around the ground and the +5V. Ground can be difficult on a JAMMA board as there are grounds on both ends! However, +5V is right next to the ground, and you should see that it forks everywhere. If it doesn't, then you're looking at the player 2 controls, and power is at the other end.