Wiring your own boat can save you considerable money. Since most boats carry a 12-volt electrical system similar to those in automobiles, the danger of serious fire or shock is very low. However, precautions should still be taken to ensure fully functioning and safe electrical equipment. Planning plays an important role in wiring a boat; good preparation can go a long way toward a simpler process.
Review the local boating guidelines on boat wiring. In the United States, the Coast Guard regulations for marine electrics fall under Title 33 CFR 183 Subpart I.
Create a diagram of your wiring layout, all on-board electronic devices and circuits, all power requirements and wire runs. Use this time to organise where devices should be located for convenience; where wires should be run to avoid fuel sources, wet areas and moving parts; and where any required switches or circuit breakers should be placed. Use this map to guide the wiring process.
Disconnect your battery completely. Run positive leads from the positive battery terminal (+) to your fuse box, and negative lines to be grounded to either the negative battery terminal (-) or the engine. Give each separate electrical device its own corresponding fuse or breaker appropriate to its amperage. Continue power leads from the fuse/breaker box to the electrical devices and connect.
Run your power wires according to the diagram and couple any wires with similar routes using zip ties and simple wire mounts in inconspicuous locations which are out of the way of standing water or moving parts according to your diagram. Run ground wires from each device to your engine or negative battery terminal following clear routes as designated on your diagram. Couple any groups of wires using the zip tie and mount method.
Connect your ground wires first, then your power leads. Test each electronic device to ensure proper function.
Always run your wiring as far away from fuel or water as possible. If there is a longer, safer route for your wiring, take it.
Fire is the most dangerous occurrence on a boat. Make sure your wiring is completely insulated so that no shorts are possible. Pay special attention near your fuel source as a spark here could prove deadly. Metal-hulled boats are conductive by nature and will require special insulated wiring to avoid shorts.