93 mazda mx6, stereo wiring?

i have a 93 mazda mx6 ls with a pioneer head unit that i install awhile ago. everything is connected correctly but there are a couple wires that i need to ask about. after i installed the head unit there were three wires left untouched the colors are: orange, brown, and lightgreen w/ white strip. the orange wire is the illumination for the head unit's lighting but my problem is the aftermarket harness that came with the head unit has no wire for the illumination wire, i was wondering what wire on the head unit can i splice into so my head unit can light up. another problem i have is that my presets don't save everytime that i take the key out of the ignition. i know its probably the ground not connected right, i have the factory wiring diagram for the car and it shows the ground wire being a black wire but when i look at the factory harness i see no black wire for ground. only a not used brown and lightGREEN / WHITE wire. is it possible that one of these are the ground for the head unit?

after i finished installing the head unit that was the very first thing i did. i've decided to go to an electronics store and just purchase a harness that comes with the illumination wire and keep it grounded the way it is which is to the chassis. thanks for the advice.