[northpole]

if you twist the constant and switched 12v together and use a permanent 12v (battery) the gauge will drain the battery... if you just connect them both up to a switched 12v if it has memory settings everytime you turn the car off you'll lose those saved to memory bits... so find a switched 12v connect the yellow to that, find a 12v permanent and connect the red wire to that. and if i'm correct the illumination wire behind the dash is gray/orange... so can be tapped into somewhere behind the dash.. the black wire( -12v) just find a grounding point it'll work as intended that way.

I can't explain it any simpler than that.

 

[northpole]

If it doesn't have any memory settings etc than your done if it does you'll have to split it. If not than it doesn't matter and you sorted it out. But keep an eye on the voltage as it might just drain the battery because the cigarette lighter is constant 12v, not switched...at least it wasn't on my mk4