Wiring a Boost Gauge, Need some help, please Options

[Dyran]

Hey all,

I was trying to avoid posting a thread on this but I couldn't find anything using the search that was much help.
So basically I'm trying to install an electrical boost gauge into my ST205. I have the sensor wires/hoses and stuff installed no worries, just having trouble with the wiring to power it and make it light up.
I've got four wires I need to tap into somewhere, they are as follows . (below is what the instructions that came with the gauge say .. )

Red - Battery (+)
Black - Engine Ground
White - Ignition Switch 12v+
Orange - Dimmer/+12v to Dimmer

Now, I can find wires to tap the Red and Black (battery, ground) wires into no worries, but I dont know where to look to find the Ignition Switch or Dimmer wires though. So if someone could point me in the right direction as to where i can find these and what colour the wires i'm looking for are, that would be much appreciated.
Thanks