What Is a JAMMA Harness (September 2026)? Complete Guide

A JAMMA harness is a standardized wiring loom used in arcade cabinets that lets any JAMMA-compliant game board plug into any JAMMA-compliant cabinet. It bundles power, video, and player control wires into a single 56-pin edge connector that matches the JAMMA standard created in the late 1980s.

If you have ever wanted to swap a worn-out Street Fighter board for a Mortal Kombat PCB without re-soldering anything, the JAMMA harness is the reason that takes minutes instead of a weekend. In this guide I will walk through what a JAMMA harness is, why the standard matters, what lives inside the loom, and how to wire one safely in your own arcade cabinet.

What Is a JAMMA Harness and Why Was It Created?

JAMMA stands for the Japan Amusement Machinery Manufacturers Association. The group released the JAMMA wiring standard in 1985 to solve a real problem in Japanese arcades: every manufacturer wired their cabinets differently. Technicians had to re-wire a cabinet every time an operator wanted to swap a game board.

The JAMMA harness fixed that mess. By agreeing on a single 56-pin edge connector with a defined pinout for power, video, audio, and player controls, two of the largest arcade markets in the world finally spoke the same wiring language. Today, almost every classic arcade board made after 1986 will drop into a JAMMA cabinet with no rewiring.

The acronym gets thrown around a lot, so here is the short version to remember.

• J – Japan

• A – Amusement

• M – Machinery

• M – Manufacturers

• A – Association

When you see “JAMMA harness” on a listing, you are looking at a pre-built wiring loom that follows this exact pinout. Plug one end into your arcade board, wire the loose ends to your power supply, monitor, and controls, and you have a working arcade machine.

Why the JAMMA Harness Standard Matters

Before JAMMA, an arcade operator who wanted to rotate games had to desolder and re-solder connections every single time. The JAMMA wiring standard turned that chore into a five-minute swap. Here are the practical benefits that still matter in 2026.

• Cross-compatibility: Any JAMMA board works in any JAMMA cabinet. Switch a Neo Geo MVS cartridge for a CPS-2 board in the same chassis.

• Faster repairs: If a PCB dies, you pull it out and drop in a replacement without touching the wiring.

• DIY friendly: A modern JAMMA harness is pre-labeled and color-coded, so first-time builders can wire a cabinet without a wiring diagram on the wall.

• Multicade builds: A 60-in-1 or 500-in-1 board plugs straight into the same JAMMA harness, letting one cabinet run hundreds of games.

• Cost savings: Restorers reuse cabinets instead of trashing them when the original PCB fails.

In our own shop, the JAMMA standard has saved us dozens of hours on cabinet restorations. The first arcade I ever wired from scratch took an entire weekend. My second one took about two hours because the harness was already in place.

JAMMA Harness Components Explained

A JAMMA harness is not a single cable. It is a bundle of pre-terminated wires that branch out from one 56-pin edge connector into the systems inside your cabinet. Here is what each part does.

The 56-Pin Edge Connector

The 56-pin edge connector is the gold-fingered plug that slides onto the matching edge of your arcade PCB. It carries every signal between the board and the cabinet. Two pin counts exist in the wild: the original 56-pin layout and a compact 28-pin version used on some bootleg boards, but 56-pin is the standard you will see in almost every harness sold today.

Note that pins are numbered from the component side of the PCB, with the solder side facing you. The same orientation matters when you wire the cabinet side of the harness.

Wire Gauge and Quality

Quality harnesses use 22 AWG wire throughout. Cheap harnesses, especially those from uncertified overseas suppliers, often use 24 or 26 AWG wire to save money. That thinner wire causes voltage drop on the 5V and 12V lines, which leads to glitchy boards, unreliable controls, and dim video output.

If you are shopping for a JAMMA harness, look for these trust signals before clicking buy.

• 22 AWG wire on the power and ground leads

• Pre-labeled wires on both sides of the loom

• Color-coded insulation matching the standard

• 0.187 inch (4.8 mm) quick-disconnect terminals for power

• 0.110 inch (2.8 mm) terminals for controls and coin door

Wire Color Coding

JAMMA wire colors are not just decorative. The standard assigns specific colors to each signal so that wiring mistakes are easier to spot. Red is +5V, yellow is +12V, blue is -5V, and black or brown is ground. Video signals use shielded coaxial cables with R, G, B, and sync on separate lines.

Pre-labeled harnesses take the guesswork out of this. The label on each wire tells you exactly which pin it terminates to and which signal it carries.

JAMMA Harness Wiring Guide

The 56-pin JAMMA pinout is the heart of the whole standard. Once you understand the layout, you can wire a cabinet from scratch. The full pinout is split into four functional groups: power, video, player 1 controls, and player 2 controls.

Power Connections (Pins 1-8)

Pins 1 through 8 carry the power supply rails that feed the arcade board. This is where the JAMMA harness connects to your arcade power supply.

• Pin 1: +5V (red)

• Pin 2: +5V (red)

• Pin 3: +12V (yellow)

• Pin 4: +12V (yellow)

• Pin 5: -5V (blue, optional on some boards)

• Pin 6: -5V (blue)

• Pin 7: Ground (black)

• Pin 8: Ground (black)

Pin 28 is also ground. Run heavy 18 AWG wire from your power supply to the harness ground if your cabinet has long cable runs, since the JAMMA harness ground wires are typically 22 AWG.

Video Connections (Pins 9-16)

JAMMA video uses analog RGB plus composite sync, which gives the bright, saturated colors classic arcade monitors are loved for. The video signals are usually shielded coax cables to keep the picture clean.

• Pin 9: Red video

• Pin 10: Key (not connected, used as a mechanical key)

• Pin 11: Green video

• Pin 12: Composite sync

• Pin 13: Blue video

• Pin 14: Vertical sync

• Pin 15: Horizontal sync

• Pin 16: Video ground

Many arcade monitors accept composite sync directly. Some require separate horizontal and vertical sync, which is why the JAMMA pinout includes both. If your monitor is fussy about sync, you may need a sync combiner circuit to merge H and V into composite sync.

Player 1 Inputs (Pins 17-28)

Player 1 inputs include the joystick directions, six action buttons, the start line, and the service test pin. Each control sits on a pull-up inside the board, so a button press pulls the signal to ground.

• Pin 17: P1 Up

• Pin 18: P1 Down

• Pin 19: P1 Left

• Pin 20: P1 Right

• Pin 21: P1 Button 1

• Pin 22: P1 Button 2

• Pin 23: P1 Button 3

• Pin 24: P1 Button 4

• Pin 25: P1 Button 5

• Pin 26: P1 Button 6

• Pin 27: P1 Start

• Pin 28: Service / Test (ground to enter test mode)

Player 2 Inputs (Pins 29-44)

Player 2 mirrors Player 1, with coin counter inputs appended.

• Pin 29: P2 Up

• Pin 30: P2 Down

• Pin 31: P2 Left

• Pin 32: P2 Right

• Pin 33: P2 Button 1

• Pin 34: P2 Button 2

• Pin 35: P2 Button 3

• Pin 36: P2 Button 4

• Pin 37: P2 Button 5

• Pin 38: P2 Button 6

• Pin 39: P2 Start

• Pin 40-44: Reserved or coin counter lines depending on the board

Coins, Audio, and Test (Pins 45-56)

• Pin 45: Coin Counter 1

• Pin 46: Coin 1 (ground to register a coin)

• Pin 47: Coin 2

• Pin 48: Coin Counter 2

• Pin 49: Speaker +

• Pin 50: Speaker –

• Pin 51-55: Reserved

• Pin 56: Test (ground to enter test mode)

Always cross-check the exact pinout printed on your harness against the official JAMMA reference, since some manufacturers shift a few reserved pins.

What Is a Kick Harness?

A kick harness is an add-on wiring loom used when the standard JAMMA pinout is not enough. Most JAMMA boards only expose 3 buttons per player through the main connector. For 6-button fighting games like Street Fighter Alpha or King of Fighters, the extra buttons live on a separate connector that goes to a kick harness branching off the cabinet wiring.

The kick harness usually has its own edge connector that plugs into a port on the game board, then splits into individual wires that route to buttons 4, 5, and 6 on each player’s control panel. If you only plan to play 3-button games, you can skip the kick harness entirely.

JAMMA+ boards are a slightly different beast. They extend the standard 56-pin connector to include buttons 4 through 6 directly, so no kick harness is needed. If you are building a multicade, JAMMA+ boards save a lot of wiring time.

JAMMA Harness Installation Tips

Installing a JAMMA harness is straightforward if you take your time. Here is the process I use on every cabinet restoration, with the lessons I learned the hard way.

Tools You Need

• Phillips and flathead screwdrivers

• Wire strippers and crimpers

• Multimeter for testing voltage and continuity

• Quick-disconnect terminals (4.8 mm and 2.8 mm)

• Soldering iron (only if you are repairing damaged wires)

• Heat shrink tubing

• Label maker or masking tape for marking wires

Safety Precautions

Arcade power supplies are not toys. A switching power supply can deliver 30 amps on the 5V rail, which is more than enough to start a fire or kill a board. Always unplug the cabinet before plugging or unplugging the edge connector.

Discharge your monitor before touching its anode. CRT arcade monitors hold a lethal charge on the anode cap for hours after power off. A grounding stick with a 1 MΩ resistor is the safe way to do this.

Testing Before First Power-Up

Before powering on the cabinet, run these checks with a multimeter.

1. Verify continuity between the power supply ground and the harness ground.

2. Check for shorts between +5V and ground. If you read 0 ohms, you have a short that will fry the board.

3. Confirm the polarity of the +12V and -5V lines. Reversed polarity will destroy most boards.

4. Measure continuity on each control line to its corresponding button terminal.

Common Mistakes to Avoid

After wiring dozens of cabinets, I have seen the same handful of mistakes cause the same handful of problems. Watch out for these.

• Buying the cheapest harness: No-name harnesses often use 24 or 26 AWG wire and unlabeled connections. Spend a few extra dollars for a pre-labeled 22 AWG harness from a known supplier.

• Forgetting the coin door wires: The coin door microswitches are not part of the main harness. You need to run separate wires from the coin switches to pins 46 and 47.

• Mixing up 4.8 mm and 2.8 mm terminals: Power wires use 4.8 mm quick-disconnects, while controls use 2.8 mm. The sizes are not interchangeable.

• Plugging the edge connector in backwards: The harness has a key slot that lines up with a gap between pins on the board. If it does not slide in easily, do not force it.

• Skipping the test mode: Most JAMMA boards enter a test menu when you ground pin 28 or pin 56. Use it to verify inputs and color before declaring the cabinet done.

JAMMA Harness vs Supergun: What’s the Difference?

A supergun is an external breakout board that lets you run an arcade board on a regular TV without a full cabinet. It has a JAMMA edge connector on one side and standard consumer video outputs on the other. A JAMMA harness, by contrast, lives inside the cabinet and is meant to stay there.

If you want to test boards on your workbench, a supergun is the right tool. If you want to put a board inside a cabinet, a JAMMA harness is what you need. Many superguns also include a built-in JAMMA harness output so you can plug into a cabinet as well.

JAMMA Harness Troubleshooting Checklist

Things go wrong sometimes. When a board refuses to boot, controls misbehave, or the picture looks off, run through this checklist before pulling the harness out.

• No picture: Check the video ground pin. A missing video ground is the most common cause of a black screen.

• Dim picture: Test the 5V line at the edge connector. If it reads below 4.9V, your power supply is sagging or the harness wires are too thin.

• Stuck buttons: Look for shorts on the control wiring. A pinched wire against ground will register as a constantly held button.

• No sound: Verify speaker polarity on pins 49 and 50. Reversed polarity gives a thin, distant sound.

• Random crashes: Check the +5V and ground connections. Cold solder joints on the edge connector cause intermittent failures.

Forum members on r/cade and Aussie Arcade have posted detailed troubleshooting logs for years. Search for your specific board name plus “JAMMA harness” and you will usually find someone who has documented the exact same problem.

FAQs

Final Thoughts on JAMMA Harnesses

A JAMMA harness is the single most useful upgrade you can make to an arcade cabinet. It turns a one-game box into a swappable platform that supports hundreds of boards, and it makes DIY builds accessible to anyone who can follow a wiring diagram. Pick a quality 22 AWG pre-labeled harness, run through the test checklist before each power-on, and your JAMMA harness will serve your cabinet reliably for years.