dead battery overnight audio system?

Thanks guys, I got an Optima Yellow Top today (Stock Battery wouldn't even jump). I hated to fork out the cash, but I installed it this evening and the car cranked. I haven't hooked up the system to it yet though, I kinda want to see if there's problems first. Thoughts... Could the built in voltage regulator in the alternator be fried? Overcharging the battery? Or more likely just too many deep discharges? The battery wouldn't hold a charge at all when I had it tested today, went up to around 12v and dropped to 9v in a matter of 5seconds. I'm just really worried this is going to happen again and kill the new battery I just bought. I can't afford for this to keep up. Could a bad ground at the head unit cause the problem? I'm still looking for ideas and troubleshooting tips as I don't think the battery was the main source of the problem, though part of it. Thanks again to all of you for your comments/ideas, much appreciated!

Update ->> OK...battery is still draining. I've identified the problem fuse to be the "Room Fuse" which is all of the interior stuff, basically. I pulled my entire dash/center console out and checked all of the bulbs/connections etc. Didn't find anything. Alternator tests good, Battery is good (Brand New). What could still be draining my battery? (My car was rear ended, small dent, a couple months ago but repaired) Could that have set off some sort of airbag/impact sensor that is draining my battery? I'm really reaching here. Any more help would be greatly appreciated. I've checked all headlights/taillights, trunk, dome, cigg lighter, etc...?

Hey Silver...thanks for the post... After leaving the car for 12-20 hours I noticed it was sluggish to turn over...so I hooked up a multimeter in series with the battery. Positive cable to multimeter/ multimeter to positive post and measured the current draw that the system was pulling when the car was turned off. (Parasitic Drain) It measured to be 150mA-160mA with an initial spike of 250mA (enough that it was making a huge spark when I touched the leads to the battery). This is far above the max recommended parasitic drain on the battery which i've read to be 50mA and specifically 35mA on my car. (A Mazda 3 2006). The image bellow shows what I have finally identified as the source of the problem. The Large Green Harness shown in the upper right corner of the fuse box is where the problem originates. When I unplug the green harness the amperage draw stops. I pulled all of the fuses in the engine and in this under the dash fuse box. None of them stopped the amperage drain. Do all of the wires in the Large Green Harness go through a fuse in this box? IF so, then there has to be a problem with either the green harness or the fuse box itself. (Since I've pulled all of the fuses and none of them solved the problem). Does anyone have ideas on how I could test each wire. And more importantly, does anyone have information on which wire is which? It's labeled "Front-1" Thanks!

jice wrote: Hey Silver...thanks for the post...

*Not Silver...sedate (sorry) My brain's fried from messing with this for the last week.