All Trussed Up
Wire should be tinned copper, which is more corrosion-resistant than common copper. It should also be stranded wire, not solid wire, and labeled "marine" on the insulation. It should also be UL-listed, loomed and supported to prevent droops and swings, and chafe-protected where it passes through bulkheads or near sharp edges. Bonus points go to boats that have dedicated conduits shielding the wiring harnesses, but make sure those wires are still accessible for service in the middle of a run.