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double check your ground, i would unbolt it where it goes to the chassis/clean up the metal and reattatch.
i assume you checked voltage with a multi-meter? if so the the 12v reading could be coming from the caps in the amp, check the fuse by the battery for continuity, sometimes the larger glass fuses will visually appear good but the soldered caps have corroded (that is the most common thing i see at our shop). unhook the battery wire from the amp and check it again to be sure.
i've seen alot of x-plode amps just die......kinda funny with the name and all, when the sony amps die they almost always blow the fuse on the amp.

i'm leaning towards no 12v+ from the battery.....