EDIT - READ POST ABOUT 4 POSTS DOWN
Well, while my ZX650.4 is out for repair, I decided I'd put the ZX1000.1 back into the car and turn on the rear fill. Just a couple days ago, the 1000.1 would drop out of the music completely. Today I took a look at it. When I turn on the H/U, voltages all look fine (~14.5 volts at the amp). When I start to crank it, though (this isn't bass heavy music either), the amp completely shut off. I turned the radio back down and it came back on in protection mode. I checked the turn on voltage - 13.5 or so. I checked the power connections, a little over 8 volts!!! I turned off the head unit so the amp would shut off, and the power rose back to about 14.5 volts over 5 or 10 seconds (car was on the whole time I was checking this).
I just bought the car about 3-4 months ago, so I don't know how old the battery is. However, let me throw this at you too. The car is supposed to have a 110 amp alternator. Well, even when the radio is off, this will happen. Say I'm driving with my lights on and heat on. Every time I come to a stop (idle), the lights dim and I can hear the fan motor slow down.
I'm assuming the battery is bad (that is, if you think my wiring is ok) if it is dropping below 9 volts when the amp is barely pulling much, but what about the alternator?