The JAMMA Connector! Copied from the old page

This is a standard in the arcade industry. Starting sometime in the late eighties, the Japanese Amusement Machine Manufacturers Association set about making a standardized game interface. This would alleviate the silliness of rewiring a cab for every new game was installed. Most games required the same inputs: one or two 4-way joysticks, 1-4 buttons for each player, coin inputs, start button, etc.

The JAMMA connector was used for almost every game produced that didn't involve a deluxe cabinet (ie AfterBurner or Virtua Racing). Generally speaking any JAMMA game can be shoved into a cabinet which previously held any other JAMMA game. There are, of course, exceptions. Many games deviated from the specification, most notably SNK's Neo Geo system, which sometimes put stereo sound out the JAMMA connector, analogue controls or other features were added, or inputs moved around. As a rule though, power and video were locked in place so you'll rarely, if ever, damage one JAMMA board by plugging it in where another was used.

A lot of Chinese-made pirate boards (Pandora's Box units) put six buttons on the JAMMA connector, using pins 26/d for button five, and 27/e for button six. It's generally harmless to swap these boards and harnesses without knowing about this, but if you put a Chinese board in a normal JAMMA harness, button six will act as if it's being held down all the time.

Roughly speaking there are only five things to connect to the game board through the wiring harness: player 1 & 2 controls, the monitor output, sound, power input and the coin-door's switches. These signals are usually grouped together. The diagram below shows the most common JAMMA pinout, and how these connections are made to the game board.

POWER
Video output
Coin door signals
Player 1 controls
Player 2 controls