18 gauge wire from battery

Connect the yellow wire to a terminal in the fuse box that is hot all the time. Dome light, cigarette lighter, headlight circuits. All you need is a constant power connection that will allow an 8-10 amp draw.

67Dart273...... actually, on modern aftermarket radios, the main power feed wire is 18 gauge, and sometimes even as small as 20 gauge, but it's only 6 inches long. They expect it to be spliced into the cars original harness right at the back of the radio. I think the wire is too small too, but it's really what is being used these days.
The other thing to know is, although most aftermarket radios advertise 40, 50, or even 100 watts per channel on the box, in actuality there are no radios that make more than about 18 watts per channel. That's how they can get away with only a 10A fuse.