How to Use Heat Shrink Electrical Connectors

Heat gun being used to heat shrink a butt connector to join a spool of sixteen gauge electrical wire to the ground lead of a trailer wiring harness

Heat-shrink wire connectors are an excellent way to easily achieve long-lasting, reliable, and weather-proof connections when wiring cars, trucks, campers, trailers, boats, and other low-voltage wiring applications.

As their name implies, heat-shrink electrical connectors have insulation that shrinks when heat is applied. Most also have an adhesive inside the insulation that seals tightly against the wire to help to make the connection weather-resistant, which in turn helps prevent corrosion.

An assortment of heat-shrink connectors, a good crimper, and a heat gun are good to have handy if you frequently make repairs to wiring. Heat-shrink butt splice connectors in particular are very handy to have around for quick and easy splices to repair wire damage due to corrosion, rodents, or other causes. They can be used for temporary or permanent repairs, depending on the situation.

Because I used heat-shrink connectors pretty extensively in my DIY trailer-rewiring project, I thought I'd add this page about the proper way to use them.

Tools Needed to Use Heat-Shrink Connectors

The most common mistake people make when using heat-shrink wire connectors (and the most common reason why the connections fail) is not using the proper tools. Using the wrong tools to crimp and shrink heat-shrink connectors will result in unreliable connections that usually will fail prematurely.

Male commercial drone pilot flying a drone at a construction site.

The most important tool you'll need to do the job right is a high-quality crimper specifically designed for use with heat-shrink connectors. Not all crimp-on wire connectors are the same, and not all crimpers are the same. Using the wrong crimper increases the chances of insufficiently crimping the connector, deforming the metal-to-metal connection, damaging the insulation, or all three.

The crimper I used for this project is the Wirefy Crimping Tool For Heat Shrink Connectors, which comes with a lifetime warranty and quality rivaling crimpers costing three or four times its price. If you regularly work with other types of crimped connectors, Wirefy also makes a Crimping Tool Set with Interchangeable Dies that can be used for literally any kind of crimp-on wire connector that I know of. It's basically the same tool, but with interchangeable jaws for different types of terminals and connectors.

Both of the crimpers mentioned above are ratcheting crimpers. Ratcheting crimpers make it easier to know when you've exerted sufficient force to get a secure connection because most of them won't open back up until you do. They also can be partially closed around the connector to hold it in place while you're inserting the wire, essentially becoming that third hand that you're always looking for.

In short, the crimper is the one tool you shouldn't economize on if you want quality crimped connections. Don't scrimp on the crimp.

You'll also need a wire stripper of some sort. You'll need to strip about 3/16 of an inch of insulation off the ends of the wires before crimping them. If you regularly work with wiring, an automatic wire stripper is a great investment that makes the job faster and easier. Otherwise, a less-expensive wire stripper / cutter will do the job just fine.

Finally, another tool you should have to install heat-shrink connectors is a heat gun. Yes, you can use a cigarette lighter or other flame-based source of heat if you insist; but you're much more likely to burn the connector, the insulation on the wires, or yourself that way. Heat guns are inexpensive and provide dry, clean, controlled heat. They're a worthy investment for do-it-yourself enthusiasts.

The Proper Way to Use Heat-Shrink Connectors

Use a wire stripper to strip the insulation on the end(s) of the wire(s) to the length of the connector's barrel. That's about a quarter inch for the pink connectors I used in this trailer-rewiring project.
Slightly twist the strands of the conductor to make them less likely to unravel when inserting them into the connector.
When using butt splice connectors, look for the seam in the metal barrel. If the crimper you're using has a convex surface on the male jaw, then position the female jaw of the crimping tool over the seam. If your crimper has flat jaws, then all that matters is that the seam be against one jaw or the other and not facing sideways.
When using connectors like ring terminals, fork terminals, or hook terminals, the seam should be positioned so it will be on top when the terminal is mounted on the post of bolt.
Position the barrel of the connector in the crimping tool and ratchet slightly, just enough to hold the connector without crimping or bending it.
Insert the wire into the barrel and completely squeeze the crimping tool to make the crimp. Most ratchet-type crimping tools will release only when the barrel is fully crimped.
Use a heat gun to shrink the insulation. This will provide both structural rigidity and a high degree of weather resistance to the crimped joint.

Video: How to Use Heat Shrink Electrical Connectors

When used and installed correctly, heat-shrink connectors provide reliable, long-lasting connections that rival those of solder, but much more quickly and with much less work. They're pretty much the only connectors I use anymore.