first off, STOP WIRING things before your car goes up in flames! if you keep "guessing" what wires are what, and just connecting wires to anything you feel like then you may start a fire or damage your car's factory wiring (which may also damage whatever is connected to it as well). if your wires are getting hot enough to 'fuse' then you're short-circuiting them or overloading them.
your head unit wiring is designed to power your head unit and ONLY your head unit. you can't just add power hungry items like a computer to it. you should have dedicated power/ground lines for your computer. if you're attempting to use the ACC line to turn the power on/off with the car then tap into an ACC circuit at the fuse box and use a relay to switch the PSU power on/off.
all you have to do to find the correct wires is open up the cig lighter plug and see where the wires connect to. the center pin/nipple is (+) and the side sliders are (-). make sure that there is no additional circuitry inside the cig lighter plug itself. if there is then you need to keep that in the circuit.