Man, you're fast!
OK, I understand part of what you're saying, but not all. I will check out that ACC line, and maybe use dual relays since I want the line to be open onlye when the car is running. So if I use one relay on the ACC and one one something like the driving lights (they only have power in on position, not ACC) that may actually work! Thanks! And now that I think about dual relays I have an even better idea: a relay that's hooked up to the starter engine's trigger voltage, so it breaks power when it's cranked! I probably wouldn't have thought about that without your suggestion!
But why a resistor? The battery is always in use since I have the stereo system and computer hooked up exclusively to that. I don't always use the computer (and my wife seldom uses it), but I always use the stereo. Do I still need a resistor?