POWERBOATER’S GUIDE TO ELECTRICAL SYSTEMS comes out the first time, don’t be afraid to do it over until you get it just the way you want it. Even if you have a good diagram already, it isn’t a bad idea to make up a new one. There is no better way to learn firsthand about all the little intricacies and idiosyncrasies of your electrical system than to trace each circuit and write it down in a diagram.
Subsystems
Fig. 2-9. A wiring harness junction located inside a locker. Not only are these difficult to find at times, but many are uninsulated, as shown here. Don’t pile all your tools into this one! A short circuit is sure to occur across the terminals.
diagram can make all the difference in the world because it will show how the wiring for each circuit is routed through the boat. A comprehensive diagram will even indicate where any of those elusive hidden junction boxes may be located.
Drawing Your Own Wiring Diagram Now that you know how to chase wires and to identify components and devices, it’s time to draw up an inclusive and detailed diagram of the electrical system on your boat. Drawing a new diagram is easier than you think, although it’s time-consuming. If you have a large boat with a complex system it’s best to divide the project up into several sessions of several hours each. If you don’t like the way your drawing 22
The first step in drawing your new wiring diagram is to mentally divide the electrical system into subsystems. These might logically be the charging and starting subsystem, the ignition and engine subsystem, the console-navigation subsystem, the lighting subsystem, and the house or utilities subsystem. Another way to do the same thing is to divide your boat physically with each division labeled as a subsystem so that the head, galley, forepeak, engine compartment, and anything else that’s appropriate for your boat becomes a subsystem. The actual division will depend on the size and the kind of boat you have, but you get the idea. Next get three or four large (11- by 14-inch is ideal) sheets of graph paper for each of your subsystems (you’ll be doing each one over several times) and a large clipboard or a piece of plywood to write on. Write the name of each subsystem on a separate sheet of the paper.
The Rough Draft For your first draft you’re going to make a separate diagram for each subsystem. You’ll put them back together for the final if you like, but for now it’s a lot easier to keep the systems in order if you keep them separate in your mind’s eye, hence the separate sheets of paper. As a logical first step, let’s start with the charging and starting circuit; it’s one of the simplest but also one of the most important. First draw a sketch of the battery symbol as it’s shown in figure 2-1 on page 13, for each of the batteries on your boat. Now label each battery with all the pertinent information you have available. This might include the cold-cranking amps and the amphours, if you know these things (much more about batteries will come later), but at a minimum it will be
