Installing aftermarket head, illumination wire?
 

Ive bought a metra kit and a BOSS BV9560B and I'm working on installing it now but im unsure of what wire i should hook the illumination and dim wires to. The metra kit comes with no such wire. The red 12V? Im weary of just slicing it and testing my luck. help me!

Forget about the dimmer wire, that is for the interior cabin lighting dimmer switch. Most car's do not have this wire leading anywhere near the stereo. As far as the illumination wire goes (when you turn on the headlights the screen will dim), the easiest thing to do in my opinion is to tap the wire into the glove compartment light. When the headlights are on, the glove compartment light is always on, so it is a good switched source.

eh, i'll just put some tape on it up and forget it. Thanks! works great!

Paimon is correct. Possibly the least headache way would be to tap the glove box light. However, the RX8 does have an illumination wire in its harness. I tapped it with my headunit. Can't remember the wire, but this diagram should help. More importantly, I'd just test the wires in the harness with a multimeter until you found the correct one. Should sit at 0V with the headlights off and +12V with the headlights on.

The most confusing and pain in the ass (deserved to be spelled out) part of all this is that there doesn't seem to be an understanding in the industry of which function should be called "dimmer" and which should be "illumination". NOR is there even a solid agreement on which color should be labeled which function. I've installed thousands of headunits. I've seen these functions/colors swap roles so many times, I just stopped even hooking them up unless it was for someone I knew. Even then, I may be able to find the wire I need in the factory harness with a multimeter, but what if the aftermarket harness has them labeled differently? I just pick one and make sure to try it out before I put the entire dash back together. If it's wrong, snip the connection and solder on the other (I like doing all my soldering outside the car, so this usually makes for a PITA too).

In the end, whichever wire is labeled "illumination" should be the wire you use. Let's just hope the manufacturer agrees.