In the same folder as the custom track. GPxPatch will find it there!
Right click and create a New Text Document.txt copy and paste the [StartingLights] and adjust coordinates.
Do not forget to save it as [track name.ini] (eg.OranPark2009.ini) which is not absolutely necessary unless you have multiple .ini in the same folder.
You can find more information by clicking help in GPxPatch or G:/Infogrames/Grand Prix 4/gpxpdata/docs/index.html
[StartingLights]
X1=-114.833
Y1=-469.958
Z1=4.865
X2=-113.44
Y2=-468.319
Z2=4.545
[ProgressBar]
Color=#1E820C
[TarmacColor]
AdjustRed=2
AdjustGreen=4
AdjustBlue=6
[PitLane]
WidthRatio=0.333
PitBoxShadow=0
[TrackMap]
data=507.250000,90.000000,639.797791,-812.912598,-78.238998,1005.690002,215.248001,-893.898010
[Tags]
Desc=Original Construction of: Oran Park, N.S.W.
Author=auscain
Created=2011
Name=Oran Park
Event=V8 Supper Cars
Country=Australia
Adjective=Astralian
Year=2009
Laps=91
lengthmeters=2620
slot=1
LapRecord=1.16.24
LapRecordQualify=1.16.24
[Corner1]
name=Dog Leg
Desc1=5th Gear
Desc2=300kmh
X=0.837
Y=0.388