//content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif Have you checked connection resistance between your front batt and rear batts to make sure there's not some random *** resistance spike on your power wire from front/rear or something along those lines? Also, resistance from your negative pole on your batt to a bare piece of frame metal should be identical from all 3 batts. Realistically, this shit shouldn't matter but unless something's causing some real voltage loss i don't have an explanation why the second amp shut itself down, as long as you weren't driving it hard into clipping.
You say the second amp won't even turn on now? Be sure the remote wire is making a solid connection and that it's receiving power? You do have fuses all over the place, right? You should have 1 under the hood on the positive wire within a foot of your front batt. Another fuse on the same wire within 1 foot of the rear batt it's connected to...and another on the wire that is actually going to the amplifier itself from your rear batts unless the amps have their own fusing and the distance is
You can check your remote wire; turn off deck. Touch DVM to remote wire set to DC VOLTS testing...turn on deck, if the remote wire is hot you'll see 12v on your DVM