Installation guide
Wiring an illuminated arcade button, terminal by terminal.
An illuminated arcade button is two independent circuits sharing one housing: a switch that tells the board a button was pressed, and a lamp that has nothing to do with the switch. Treating them as one circuit is the source of most wiring faults.
An illuminated arcade button has two separate circuits. The micro switch uses the COM terminal wired to a shared ground and the NO (normally open) terminal wired to that button's input on the encoder or JAMMA harness; the NC terminal stays unused. The 12V LED is a second, independent circuit with its own two terminals and its own polarity. The lamp is not powered by the switch, so a button can read correctly while unlit, or light while reading nothing.
The micro switch: COM, NO and NC
The switch body carries three spade terminals. COM is the common pole. NO is normally open — the circuit completes only while the button is held down, which is what an arcade input needs. NC is normally closed and passes current until the button is pressed; it is used for interlocks and door switches, not for player inputs, and on a control panel it is left disconnected.
Wire COM to the shared ground and NO to the input pin for that button. Getting COM and NO reversed does not damage anything, but the input reads as permanently held, which usually shows up as a game that will not leave the attract screen.
Daisy-chaining the common ground
Every switch on the panel shares one ground. Rather than running a separate ground wire from each button back to the board, run a single daisy chain: a short jumper from the COM of the first button to the COM of the second, and so on across the row, with one wire from the end of the chain back to the ground pin.
This is standard practice because it cuts the wire count roughly in half and keeps the loom serviceable. The one rule is that the chain must be continuous — a single unseated spade partway along kills every button downstream of it, which is why "half the panel stopped working" almost always means a loose common, not a failed board.
The lamp circuit and polarity
The lamp is separate. On 12V LED buttons the two lamp terminals are polarised: positive to the 12V supply, negative to supply ground. Reversed, the LED simply does not light — it is not damaged, which makes a swap the first thing to try on a single dead lamp.
Incandescent lamps in older machines are not polarised and will work either way round, so a machine being converted from bulbs to LEDs will often come up with a scattering of unlit buttons purely because the original loom paid no attention to which wire went where. Check the supply voltage before connecting: a 12V LED on a 5V rail will be dim or dark, and on a higher rail it will fail quickly unless the button has a resistor fitted.
Fault-finding in order
Work from the symptom. One button dead, lamp fine: the switch or its spade connector. One lamp dead, button fine: LED polarity or that lamp's pair of wires. A block of adjacent buttons dead: the common ground chain, checked from the last working button forward.
All buttons dead but lamps lit: the ground return to the board, or the board itself. All lamps dead but buttons fine: the 12V supply rail. Splitting the fault by circuit first — switch side or lamp side — resolves most panels without a meter.
| Terminal | Circuit | Connect to | Notes |
|---|---|---|---|
| COM | Micro switch | Shared ground, daisy-chained | Common pole for the switch |
| NO | Micro switch | Button input on encoder or harness | Closes only while pressed |
| NC | Micro switch | Unused on control panels | For interlocks and door switches |
| LED + | Lamp | 12V supply | Polarised; reversed means no light |
| LED − | Lamp | Supply ground | Independent of the switch circuit |
Frequently asked questions
Which terminals do I use on an arcade button micro switch?
COM and NO. COM goes to the shared ground and NO goes to that button's input. NC is left unconnected on a player control panel.
Why does my arcade button work but not light up?
The lamp is a separate circuit from the switch. Check LED polarity first — reversing the two lamp wires fixes most single dead lamps — then the 12V supply rail.
Do arcade button LEDs have polarity?
Yes. 12V LED buttons are polarised: positive to 12V, negative to ground. Reversed they do not light, but they are not damaged.
Why did half my buttons stop working at once?
Almost always a break in the daisy-chained common ground. Check the spade connectors starting from the last button that still works.
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