in any case if your unsure, Just make sure theres a fuse between each power wire, so if somthing happend between the rear and front bat, the fuse would blow, and if somthing happend between the amp and rear bat, the fuse would blow, so in any situation, just make sure all power wire is fused like lets say the main bat is under the hood, there would be a fuse there close to the battery, then if u have another wire back to the other bat, and a wire to the amp, there would need to be a fuse between the other bat and amp