When it comes to working on your vehicle’s electrical system, even seasoned professionals get frustrated. Intermittent problems, under-dash harnesses that look like spaghetti, and years of patches and “get it home” fixes, usually just make things worse. In our experience, about 90% of all electrical issues turn out to be a bad connection.
Crimp terminals are efficient and work well and in some cases required, but over time, corrosion can set in and cause problems with the connection. Soldering is the best bet for an enduring repair, so knowing how to solder wires correctly can be a worthy skill to learn. The trick to soldering is making sure that the joint is fully heated through and not a cold-solder joint. A cold solder joint happens when the hot solder hits a cold wire, hardening it. It can look like the joint is good, but in reality, the solder is only on the outside of the wire, and not pulled all the way through the wire strands.
When soldering, there are a few tips and tricks to get the best connection possible. These tips work on any soldered wire connection. When soldering, it is always a good idea to disconnect the wires from the electronics whenever possible, as the heat can easily transfer to the electrical components.
Crossing the Streams
There is one way to twist wires together for soldering- a horizontal twist that yields a continues length of wire. A pig-tail, where the wires are bent at a 90-degree angle to the rest of the wire is NOT a suitable connection and will cause problems, don’t do it.
Heat Don’t Lie
The best way to know if your solder joint is hot enough is when you can see the strands of the wire in the solder itself. Always place the soldering iron or gun UNDER the wires and add the solder to the TOP of the wire. Solder is attracted to heat, so as the solder melts, it is pulled towards the heat, through the wires, connecting every strand together with solder.
I Scream, You Scream, We All Scream for… Tubing…
You can’t just leave a soldered connection uncovered, it is a live circuit. Electrical tape is OK, but most people don’t use good-quality tape. The best solution to cover soldered wires is heat shrink tubing, and it must be installed BEFORE the soldering is done. Once the solder has cooled, simply slide the tubing over the joint and use a lighter or heat gun to shrink it. Just make sure you use the right size for the wire.
If you have to use electrical tape, and sometimes you can’t avoid it, there is one specific brand and model you need- 3M Super 33 or Super 88. This is not a joke either. $1-per roll tape is junk, and absolutely should never be used on electrical connections unless it is an emergency repair. Super 33 and Super 88 is about $4-5 per roll, and it goes on, sticks to and seals the connections without falling off four months down the road. Super 33 is the standard in the professional industry, and you should keep a roll in your tool box at all times. The cheap stuff is for bundling wires, and to hold the towel on your hand when you cut off a finger, that’s about it.
If you follow these tips, your electrical repairs will last forever and provide years of worry-free service. If you don’t, well, then you will probably be back under the dash on the side of the road, doing your best origami folded human pose, wishing you had just soldered it in the first place.
Check out all the tools & equipment
A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.