Frontline pinout:

             "G"                                         "T"
1 GND                    A GND                    1 GND             A GND
2 VIDEO RED              B VIDEO GND              18 +5
3 VIDEO GREEN            C VIDEO BLUE             REST ARE N/C
4 COMPOSITE SYNC         D N/C                     
5 + AUDIO                E AUDIO GND
6 N/C                    F N/C                           "H"
7 MRST                   H N/C                    1 GND
8 COIN SW RIGHT          J COIN SW LEFT           2 GND 
9 TOP COIN COUNTER       K BOTTOM COIN COUNTER    3 N/C
10 RIGHT COIN LOCKOUT    L LEFT COIN LOCKOUT      4 N/C
11 SERVICE SW            M SLAM                   5 +5
12 1 PLAYER SELECT       N 2 PLAYER SELECT        6 +5
13 JOY UP                P N/C                    7 N/C
14 JOY DOWN              R N/C                    8 N/C
15 JOY RIGHT             S N/C                    9 +12
16 JOY LEFT              T N/C                    10 KEY
17 GUN UP                U N/C                    11 +12
18 GUN DOWN              V N/C                    12 +12
19 GUN RIGHT             W N/C                    
20 GUN LEFT              X N/C
21 FIRE                  Y N/C
22 JUMP                  Z N/C