well i'm an employee at best buy and i had it installed by them. wiring could be the problem because the HU is in the center console and does shake a little bit from the bass, so it could be vibrations. i'll take some pics later.
as far as my voltage drop goes, i don't have a voltmeter so i couldn't tell you what the voltage drop is exactly, but my headlights dim pretty bad even when driving
take a dmm and meter it with the music on then let us know