Do not use wire nuts to repair electrical wires on a car, such as battery wires, speaker wires, oxygen sensor wires, ignition coil wires, etc. Wire nuts are for repairing electrical wires on homes where there are no constant vibrations or corrosion issues. Wire nuts should never be used to repair wires because they can come on due to vibrations felt on a car, such as when hitting speed bumps.
Another reason why you should not use a wire nut in-vehicle applications is that a wire nut may not thread properly into soft wires used in cars. Instead of treading to the car wires, a wire nut will crush the electrical wires found on cars making the connection weak.
The fastest way to repair car wires is to hold the two wires so that the bare wires cross at an angle. Twist the two wires tightly together, then use electrical tape to insulate the connection.
The ideal method to repair car wires is to solder and heat shrink application. This takes a little bit of skill, plus requires a soldering iron and patience. Soldered connections are a permanent repair and do not suffer from corrosion or continuity issues in the future. Auto mechanics and car dealerships use this method or at least should.
Another fix is to use crimped butt connectors. Crimped button connectors provide great longevity but can sometimes have issues down the road. They are not impervious to vibrations or corrosion, especially if the wires are exposed to the elements. Also, if the butt connectors are not made properly,y the connection can easily fail shortly after the repair.
A temporary fix is to use the twist and tape metho,d, which will certainly make the connections and wor. Overtime can lead to continuity issues and corrosion, which leads to things intermittently working.