How to Make Watertight Electrical Connections in a Boat 

Electrical problems on a boat are usually caused by bad connections. Weak connections or those that aren’t adequately sealed are prone to corrosion, and can come loose or fail altogether.

To ensure your boat’s electrical system is protected from corrosion and burnouts, you need to make sure all electrical connections are robust and watertight. Here are some tips for making watertight electrical connections on your boat. 

Tools For Making Solid Electrical Connections

Quality electrical tools enable you to make watertight electrical connections that are safe, secure, and long-lasting. The following tools are essentials for making solid electrical connections for your boat and its engine.

Wire Stripper

This tool removes the insulating jacket from the wire without cutting any of the strands or the cable itself. Dedicated wire strippers have scales for precision, and are less expensive and easier to use than stripper/crimper multitools.

Crimper

A crimper capable of making precision F crimps is easier to use, more accurate in difficult-to-access spaces, and delivers better results than a stripper/crimper multitool.

Heat Gun – Butane Torch

Heat guns and butane torches seal heat-shrink tubing around electrical connections. A heat gun offers excellent heat control, but requires an electrical power source. On the other hand, a butane torch doesn’t require a power source, is more maneuverable and can get into tighter spaces, but requires greater care to avoid burning through wiring insulation.

Making Watertight Electrical Connections

Use Boat Cable/Marine Wiring

Always use boat cables when installing new wiring. Boat cable is made of multi-strand copper wiring that has been “tinned” to withstand the harsh marine environment. The marine-grade wire is flexible and resistant to boat vibrations, while the “tinning” means the wire strands are coated to protect the copper against corrosion. 

Check for Corrosion

Look for signs of corrosion when making new electrical connections with the existing wiring on your boat. Remove some of the insulating jacket from the terminal end of the wire and inspect it. If it’s silvery (boat cable) or pinkish (copper wire), the wiring is free of corrosion and can be reused. However, if the wire is blackened, it has started corroding. Strip away more of the insulating jacket until no more corrosion is evident, and cut away the corroded section of wire. If the corrosion is severe, replace the wire.

Strip the Cable

Strip enough insulating jacket from the cable so that when the cable is fully inserted into the butt connector or ring terminal, there’s no metal wire exposed between the connector/terminal and the cable.

Butt Connectors and Ring Terminals

Use butt connectors and ring terminals with nylon insulating jackets. Nylon is UV-resistant and won’t get damaged by fuel or oil. Vinyl and plastic insulating jackets don’t provide the same protection as nylon jackets, and they’re prone to hardening and cracking over time.Get butt connectors and ring terminals that come with their own heat-shrink tubing, which makes installing new cables much easier. 

If the connectors or terminals don’t have heat-shrink tubing, slide some over the cable before crimping it to the connector or terminal.Tinned copper butt connectors and ring terminals are recommended, as they’re coated to protect the copper against corrosion. Make sure the butt connector or ring terminal is matched to the wire it’ll be crimped with. 

NOTE: If the connector or the lug of the terminal is too big for the gauge of the wire, there will be air pockets within the crimp, which will create voltage resistance within the electrical circuit, and generate heat that will reduce the lifespan of the cable and connector. If you trim strands of the wire so it fits into a smaller connector or terminal lug, the resistance becomes less predictable and the electrical circuit will be unreliable or fail completely.

Crimping Electrical Connections

Using a crimper, apply enough pressure so that the crimp creates solid metal-to-metal contact between the wire and the butt connector or ring terminal. 

If possible, make two crimps to ensure a solid bond between the wire and the connector/terminal. Never solder wires to butt connectors or ring terminals. Test the crimp by pulling the wire away from the butt connector or ring terminal to make sure the electrical connection is strong.

Waterproof the Electrical Connection

The best way to ensure an electrical connection is waterproof is to heat-shrink the connection. Gently heat the heat-shrink tubing with a butane torch or heat gun until it shrinks over the crimp to form a watertight seal. An alternative to heat-shrink tubing is liquid electrical tape, which is a rubberized insulation that is painted onto an electrical connection and creates a flexible protective coating. Apply at least two coats of liquid electrical tape to an electrical connection, allowing several hours for the first coat to fully cure before applying subsequent coats.

NOTE: Liquid electrical tape isn’t as robust as heat-shrink tubing and therefore not recommended for electrical connections in the bilge or other areas that get wet. However, liquid electrical tape is great for quick, temporary repairs, and keeping some on board may help get you back to shore in an emergency.

Zip-Tie the Cables

Loose cables can easily get snagged, causing wires to get damaged or being pulled from their connectors. Use zip ties for every 18-inches or so to keep cables bunched together, and to attach the cable runs where they pass through bulkheads, or to keep the cable runs out of the way. Make sure you leave some slack in the cables so they don’t become stretched as the boat moves and flexes.

Watch the video above to see how to make wiring repairs on the charging system of a Mercury 40 outboard engine.