[soapbox]
I am a firm believer that all car stereo wiring should be carefully soldered and shrink-tubed (note: not just wrapped in tape because that comes undone, too). If you're not prepared to solder and shrink-tube the wiring connections on your car stereo installation, it's time to hire a professional to do the job. Period.
[/soapbox]

Amen, actually I used self-amalgamating tape. It sticks to itself and doesn't come undone. It's just a little quicker and easier than shrink tube.