08 mazda 3 s wiring

Hi I have a wireless reverse camera on my M3 and the head unit has a wire that takes +12v as a trigger for switching to the r-cam input. I would like to wire this up but I am having issues figuring out where I can tap the reverse light at the front of the car. I looked at the wiring diagram and it says it could be the GREEN/ orange or the GREEN/ black. I found 2 GREEN/ orange cables in the passenger kick, one is thick one is thin and I am not sure about the GREEN/ black it may or my not be in there it's really hard to tell. I don't want to start cutting into wires willy-nilly and was hoping someone with experience could give me an idea of how to deal with the rats nest they have in there. Thanks guys.

did you test any of them? that'd be a good starting place. A DMM is a beautiful thing.

MECP Advanced Installer Certified.

How should I go about testing them? Strip off some insulation and test for voltage to ground? I don't want to end up shorting out something important or setting off an airbag or something stupid :P I'm new so these might be some pretty basic questions but I've never really worked with car wiring before. Sorry for my ignorance. Thanks.

yeah just get a multimeter set it to dc voltage and put the red lead to the wire you're testing, and the other to ground and put it in reverse. if you get 12 volts or so when put into reverse but no other position then that is it.A DMM is a beautiful thing.

MECP Advanced Installer Certified.