Yes, apparently there is a distinct difference. Automotive wire is multiple strands of copper conductors covered in a thin PVC jacket of insulation, perfect for your average Chevy, Buick, or Ford motor car. “Marine wire” on the other hand is unique in that it is made up of many more smaller strands of copper wire, each coated in a micron’s thickness of solder before being ever so carefully over-coated in yet a thicker jacket of PVC insulation.
This process adds both corrosion resistance, and increased flexibility in the harsh marine environment. It also adds nearly double the cost per foot. In the era of 1977 Taiwan boat building they thought it prudent to use automotive grade copper wiring, and as you can see from the picture, after 36 years the factory wiring has begun to oxidize and turn green inside of the insulation. This oxidation creates resistance, which in turn creates heat , which causes insulation to melt, which causes short circuits in the DC electrical system.
The plan all along was to rewire the entire boat along with a new breaker panel, moved out from under the companionway steps and relocated to the right of the nav station. Now that we’re into the headliner & insulation project, might as well start with the overhead cabin lighting. Simple, in that it’s only isolated to “Forward” and “Aft” lighting circuits. One black wire for a common ground (-), one red wire for aft cabin lights (+), and a purple wire (+) for forward cabin lights; all of it #12 AWG automotive wire. Based on our planned conversion to LED bulbs and fixtures and the anticipated current draw on our battery system (without burning the boat down in a fiery blaze), I’m pretty confident that #14 AWG marine wire will work as a suitable replacement. We shall see…..
Previous owners installed (and I use the term “installed” loosely) various strip fluorescent lighting fixtures over the settees for additional reading lights. None of it was (of course) the proper type, color, or diameter of wire thats supposed to be used, and all of it was connected by twisting bare strands together and wrapping the “splice” with electrical tape. This would almost be funny if it wasn’t such a potential danger. Luckily, it’s the low voltage DC lighting system, so the worst that could happen is a blown fuse, a short circuit, maybe some melted wire insulation, or possibly a fire, resulting in our entire life’s savings resting on the bottom of the ocean.
By the way, if you plan on doing what Jeni & I are doing, and you haven’t read Nigel Calder’s book “Boatowner’s Mechanical and Electrical Manual” yet, I strongly urge you to dump the $50 into this book. It’s worth every penny.