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4awg here and 0 to the ground block. I figure that in a marine environment where the engine may not be running for extended periods of listening, give the amp the ability to draw all it can.

now...

personally, use 0 gauge, use only one, and make it a somewhat short lead. I used 0 and they are around 2.5ft total length from battery to dist. block, running 3 med-sized rockford fosgate power...