Usually the lighting will use a red wire that connects to the dimmer, and a black wire that connects to the chassis. Some use a 12V feed from the ignition switch that is drained through the sensor in the engine bay, to get a sensor readout by measuring the sensor's electrical resistance.
Ah... A chinese-made gauge! *Laugh* "Thank you, for to buy our most excellent turbo air gauge of pressure!"
By 'ignition', they're probably referring to switched 12v power. See what happens by just grounding the gauge, and touching the red and yellow wire (and then both) to a 12V source and see what happens.