Originally each button was soldered to a gaming controller. This worked just fine using button mapping, but recently [Dossier] made the switch to using an Arduino Leonardo. This is a perfect choice.

CUI Devices has introduced dozens of illuminated tactile push button switches, in packages as small as 3.4 x 3.4 x 1.5mm. Colours span blue, green, red, red-blue, red-green, white and yellow, and ...

The push-button ignition is one of those buttons that doesn’t really add any new functionality over the thing it’s replacing (in this case, the ignition system that has you insert and turn a key).