JAMMA connector pinout
Pin pitch is .156 in (3.96mm). There are 28 pins per side, 56 per board.
Infos from [HardMVS.com]
| GND | A | 1 | GND |
| GND | B | 2 | GND |
| +5V | C | 3 | +5V |
| +5V | D | 4 | +5V |
| E | 5 | ||
| +12V | F | 6 | +12V |
| Key | H | 7 | Key |
| Coin counter #2 | J | 8 | Coin counter #1 |
| Lockout coil #2 | K | 9 | Lockout coil #1 |
| Left speaker + | L | 10 | Right speaker + |
| Test switch | M | 11 | Mono audio + |
| Video green | N | 12 | Video red |
| Video sync | P | 13 | Video blue |
| Service switch | R | 14 | Video GND |
| Coin switch #4 P2 | S | 15 | Coin switch #3 P1 |
| Coin switch #2 P2 | T | 16 | Coin switch #1 P1 |
| P2 Start | U | 17 | P1 Start |
| P2 Up | V | 18 | P1 Up |
| P2 Down | W | 19 | P1 Down |
| P2 Left | X | 20 | P1 Left |
| P2 Right | Y | 21 | P1 Right |
| P2 A | Z | 22 | P1 A |
| P2 B | a | 23 | P1 B |
| P2 C | b | 24 | P1 C |
| P2 D | c | 25 | P1 D |
| Select down | d | 26 | Select up |
| GND | e | 27 | GND |
| GND | f | 28 | GND |