the wire your looking for is:

grund or open when the car is off
ground or open when the car is on
12v when the headlight or parklight is on
if it has 12v on the headlight or parklight wire, adjust the dimmer, if it fades from 12v to a lesser value, you are on the dimmer wire...which is the wrong wire.

if you do not understand this post, you should't install a head-unit...

__________________
Triple Point Certified Judge - DB Drag Racing
Street A - 154.1 db *certified
Super Street NW - 154.2 db *certifed
Canadian Record...
USACi Pro Stock 2501-5000 watts - 155.9 db
Canadian Record...
IASCA Pro STK 1 - 154.8 db
Canadian Record...

'04 World Champion 0-600 Pro Basic
'04 Best of Show
'05 World Champion 0-600 Inter. Pro
'06 Installation Judge World USACi Finals
'07 DB Drag World Finals 2nd Place - San Mateo, California
'08 DB Drag World Finals 1st Place Laughlin, Arizona
Rep. for USACi in Canada