Just to clarify since people have been saying that there's a "common ground" for the lamps, that diagram would indicate that the lamps are low-side-switched. This is pretty typical. You supply a common power rail (+5V, according to the diagram) and the switch the return path to ground on/off for each lamp.
Handily for you, this is compatible with things like an LED-Wiz, Pac-Drive, etc.
(You can probably flip it around if you want to high-side switch it - just check that it won't hook anything up you don't expect)