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How To Make The Perfect Crimped Connections

Many electrical problems on boats are due to poor connections. Here's how to make perfect crimped joints.

Wiring on a boat leads a hard life. Corrosion, vibration, and chafe all conspire against your boat's electrical system to bring it to unexpected failure or premature end. Bad connections are to blame for many problems, but knowing how to make proper crimped terminals will go a long way toward avoiding issues. Simply twisting wire together, using wire nuts, or wrapping cable around a terminal screw will not do. Proper crimped terminals are neat, allow the free movement of electricity, are resistant to moisture intrusion, and prevent open and short circuits.

Before making a connection on your boat, take a few practice runs on some spare pieces of cable so you're able to make perfect joints every time. Terminals and cables come in a variety of sizes measured by what is called "gauge" – the smaller the number, the larger the cross-sectional area of the cable conductor, which means that it can carry higher electrical loads. Use cable that's correctly sized to match the maximum current it will have to handle. Err on the side of too big. Finally, only use multistrand tinned marine cable on a boat. Untinned cable is cheaper but very susceptible to corrosion.

Tip: Planning to do much boat wiring? Invest in a good set of ratchet crimpers. They make a nice double crimp, and the ratchet action means they won't release until sufficient pressure has been applied.

You don't need many tools: crimping pliers, wire strippers, and a heat gun should do it. You'll also need cable, crimp connectors or terminals, and heat-shrink tape or heat-shrink connectors of the right size (keep a selection of sizes available). Some connectors and terminals come with heat-shrink that includes a sealant for water-tightness. Note that while our purpose here is to show you how to fashion properly crimped terminals, this is also relevant to other applications, such as using butt-end connectors.

Tech Support

Degree Of Difficulty: Easy

Tools and Materials:

  • Crimpers
  • Wire stripper
  • Side cutter
  • Hot air gun
  • Wire
  • Heat shrink
  • Terminals

Time: 5 minutes.

Cost: Minimal.

Cutting back ragged edge

1. Cut back any ragged ends of the wire using a pair of side cutters or the cutters built into the crimping tool.

Stripping off insulation

2. Strip off the insulation from the wire. Cut only through the sheathing and not into the actual wire. Notice that the wire-stripping tool has a reference scale that corresponds to the wire gauge. Remove only sufficient insulation to allow the wire to be entered fully into the terminal, leaving no bare wire visible.

Twisting wire strands

3. Grasp the wire in one hand. Twist the strands together between your other thumb and forefinger to bind them tightly together. This makes it easier to push the cable end into the terminal.

Cutting heat-shrink wrap

4. If you're not using a connector with built-in heat-shrink, cut a length of heat-shrink about 1 inch long, the same color as the cable insulation. Slip this onto the wire.

Terminal connector

5. Slide a terminal connector onto the end of the cable. Ensure that it's pushed fully home, then use the crimping pliers to squeeze it onto the wire. Note that the crimping jaws are color-coded. The colored dot on the plier jaws should correspond with the color of the terminal.

6. Tug on the connector to test the integrity of the joint. If there's any movement or the terminal comes off, cut back the cable and start again. Slide the heat-shrink back up the cable so it covers the crimp completely. Then use a hot-air gun or a match to shrink it into place. The same applies to connectors with built-in heat-shrink. Use only enough heat necessary to shrink it to the cable.

Finished connector

7. Congratulations! This perfect electrical connection should give you years of trouble-free service.

Bad Connections, Big Problem

From our claims files, here are five ways bad connections can create problems aboard:

Loose connection

No power. A bad connection may look fine from the outside, but what's inside may not be a connection at all. If the wire isn't in a crimp connector all the way, your connection may not work. Note: A crimp connector is the only kind that should be on your boat.

Wire nuts cause boat fire

Intermittent power. One of the most frustrating problems to chase down is a lack of power to a component, especially when it sometimes works. Known as intermittents, these happen when the connection is not tight or has corrosion inside. These wire nuts (don't ever use these aboard) are exposed to water and will eventually fail — or fail sometimes.

Bad battery terminal connections

Fire. Overloading circuits can result in a fire. Whether they're improperly fused, or have too many connections as in this picture, overloaded wires will heat up and catch fire — and burn anything near them.

Internal corrosion. Poor connections on the boat's bonding system can cause corrosion on things such as thru-hulls and seacocks. Because these are often in damp environments, special care has to be taken to inspect them. A quick tug is often all it takes to check for a strong bonding wire connection.

Bad lower unit

External corrosion. Outdrives with impressed current anode systems (such as the Mercury Bravo 3 and some Volvo outdrives) depend on a good, clean electrical connection to prevent corrosion of underwater metals. If this connection fails, your very expensive outdrive is at risk.

— Charles Fort

Mark Corke

A marine surveyor, and holder of RYA Yachtmaster Ocean certification, Mark has built five boats himself — power and sail. He was senior editor of Sail magazine's hands-on "Boatworks" publication, worked for the BBC, written four DIY books, skippered two round-the-world yachts, and holds the Guinness World Record for the fastest there-and-back crossing of the English Channel, in a kayak! He and his wife have a Grand Banks 32.