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How to Splice Automotive Wires

Use a professional tool and moisture sealant for first-class results

Use a professional crimper and electrical moisture sealant to make quick, solid connections in auto wiring.

By the DIY experts of The Family Handyman Magazine

Splice automotive wires in seconds

Photo 1: Crimp the connector

Strip the insulation so only the bare wire is inside the connector. Then make a single 5/16-in. crimp on each side of the butt connector.

Photo 2: Cut the moisture sealant

Cut a section of moisture sealant to cover the entire connector and a 1/2-in. overlap on each end.

Photo 3: Seal the splice

Then double it over and squeeze it together with your fingertips.

Crimp-on wire connectors work well if they’re crimped properly (a 5/16-in.-wide crimp) and sealed (usually with heat-shrinkable tubing). But most cheap crimping tools only make a 1/8-in. crimp, so you’d have to make four of them for a simple butt connection.

Invest about $25 in a professional crimping tool (OTC No. 4497 from Then buy a roll of electrical moisture sealant (3M No. 06147; about $20 from Then just follow the steps in Photos 1, 2 and 3.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

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