The exhortation to “solder and shrink-wrap it” was drilled into my head as well during many of the electrical service training classes I sat through as a journeyman tech. At the time, a soldered joint was considered superior, more professional and certainly more durable than simply twisting the wires together and covering them with electrical tape or using one of the pliers-operated plastic splice connectors of the day. Much has changed since then, which is why many vehicle manufacturers recommend crimped, rather than soldered connections when it becomes necessary to make a repair to a wiring harness. Let’s look at some of the reasons for this change in policy. The first that comes to mind is electronics. Soldering takes heat, and many electronic components can be damaged by being exposed to too much of it. If your soldering takes place near an electronic component, heat sinks must be used to absorb excess heat and shield the adjacent component from damage. There are many locations where this just isn’t practical, which is why a crimped connection is preferred. In a soldered connection, the wires are stuck together by the solder. In a crimped connection, the pressure of the crimp removes the gaps between the wires and literally fuses them together. Though crimping effectively reduces the cross section of a wire by about 20%, the small resistance added amounts to an essentially unimpeded electrical flow across the crimp. With a soldered joint, there is only minimal contact between adjoining wires. Consequently, the main electrical path is through the solder, rather than the wire. The solder has more resistance than the copper wire, which means the solder joint creates a small voltage drop at that point. In large-gauge solder joints that handle high current loads, this voltage drop may create a “spark-gap” condition, where the heat generated by the solder’s resistance could be enough to melt the surrounding insulation and set it aflame. The heat of soldering also causes wire embrittlement, strand fatigue and corrosion. Wires tend to flex near soldered joints, increasing the chance of breakage and corrosion, particularly after heating. This set of circumstances probably caused the second failure of the wiring repair on your customer’s station wagon. The crimping pliers should grip the crimp connector, then compress it in a controlled fashion that fuses the wires into a solid mass. The wrong crimping tool may smash the connector instead, possibly damaging the crimped wire in the process and setting things up for a repeat failure. Prepare the wire for the splice. Remove only enough insulation to allow a snug fit of the exposed wire in the crimp connector. The wire must be clean and bright, and free of any corrosion or other contamination. The crimp connector must match the wire gauge of the wire to be crimped. If the crimp connector is too large, the crimping pliers won’t be able to crimp the connector sufficiently to create an effective joint. Smashing a too-large crimp connector in an attempt to match it to a smaller wire gauge won’t work. Use an uninsulated crimp connector and cover the finished crimp with shrink tubing. The tubing’s main job is to keep out moisture and electrically isolate the joint, but it also provides a measure of mechanical strength to the wire section it protects. A crimp joint protected by shrink tubing is less likely to flex and break. There are certain cases where no type of wiring repair, be it soldering or crimping, should be attempted. This would include air bag and ABS wiring, as well as shielded wiring for such components as speed or knock sensors. In the case of safety systems, damaged wiring must always be replaced with an undamaged wiring harness, to assure that the system will perform as designed under emergency circumstances. Simply put, your shop should not assume the liability for a safety system failure brought about by a faulty wiring harness repair. If the harness is damaged, insist on harness replacement and decline the repair if the vehicle owner objects. News source: Motor