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Hi, I was looking at the DIY for audio wiring and would like to know what the state of each wire is doing when the ignition is off with no power, when ignition is off with power and when the ignition is on.

I know the radio still uses some power because it has to retain your radio settings, right? Does power run thru the 12V wire all the time? Or is it a different wire altogehter? What is the switch wire? And is the illuminate on only when you've got your headlights on or does it come on the moment you turn your key? I'm so confused. Please help.

I want to install a small PC into my car but I don't want it to shut down instantly when I turn off my car.

RADIO 12V white/red + radio
RADIO GROUND black - radio
RADIO SWITCH yellow/red + radio
RADIO ILLUMINATE red/black + radio

 
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yellow wire is constant 12v (memory)
red and white is accessory (switched)

 
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Radio illuminate, illuminates your oem headunit when you turn your headlights on.

If you plan to use a aftermarket hu, it would make things easier for you if you use a wiring harness, that will definitaly come in handy when you want to sell your car.

If you want to install a PC in your car you will need to connect it to your battery or another constant powersource. You will also need a power inverter, which can be bought at any Futureshop, Crappy Tire, Best Buy, etc. That inverter plugs directly into your 12 V socket.

 
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Hey, MrWong... You live in Edmonton too? Anyway, the thing I'm looking at is not a normal PC (search PC104). It can support various Pentium/Celeron and x86 CPUs however and I think they can take either a 5 volt or 12 volt power source with max current of 1 amp and max power of 12.6 watts (see here).

But the power inverter will help me for another project (see www.cappuccinopc.com and www.5speedpc.com). I'm not an electrical guy in any sense. What I knew I lost long ago.

 
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If those PCs can support 12 v, then all you would need to do is connect it to a constant power supply (eg your main battery or secondary battery).

That way the PC will not shut down as soon as the car is off, you can also install a main power switch installed that will allow you to cut power to the PC at anytime. You can mount the switch any within easy reach in the drivers cockpit.

It would also help if you get a thicker guage wire (8g or 4g), if possible, for connecting your PC to the power source as well as a fuse, the fuse will protect the PC from powersurges in the event they happen, in between the battery and the PC.

The wiring process should be very similar to hooking up a amp for your in car audio.