Standard arcade wiring from most major manufacturers is AWG22 stranded. It's a handy size and fits onto standard red crimp connectors very reliably. It will also stand up to repeated vibration and flexing found in arcade games better than solid will. It's generally bundled into harnesses using zip ties. The harnesses can be bound to surface backs (bottom of control panel, side of cabinet, etc.) using either screw down zip-ties (this is a zip tie with a screw eyelet on one end), stick-on strap-ties, etc.
For power to JAMMA boards, AC, etc. usually AWG18 stranded is used. Grounds for signals (e.g. buttons, joysticks, etc.) are still usually AWG22 as it carries essentially no current.
Any smaller than AWG22 won't hold in crimp connectors reliably and may not even hold into the terminal block on the IPAC correctly. Solid also doesn't crimp right and is susceptible to breaking, especially right where connections are made as that's a stress point.