I turned on the headlights and dash lights at night time, and turned the radio up darn loud. The lights on the deck were sure dimming, and I could barely take the noise, but the headlights and dashlights stayed steady.
Seems okay.
BTW: When I have my headlights on, and I switch on the AC, they dim a little bit, and stay dim. Just BARELY dimmer, to where you can only tell the difference at the moment you hit the AC button. Is this normal or a sign of a dieng arternator?