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Wiring Fundamentals: Soldering

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00:00 - The use of solder in automotive wiring harnesses is a hotly debated topic.
00:04 With one side stating that it is far more reliable than a mechanical crimp connection and provides for a better electrical connection.
00:11 The other side stating that its use should be very limited as it creates brittle connections that are prone to failure when subjected to continued vibration.
00:19 My experience puts me in the second group as I have seen many failed solder connections but far fewer failed mechanical crimp connections.
00:27 At the top tiers of motorsport wiring harness construction you will find almost no situations where solder is used.
00:33 And if it is required, very careful attention is paid to mitigating damage from vibration and providing strain relief.
00:40 We'll look at an example now of a situation where soldering is acceptable.
00:44 That of making a connection to a d-sub nine connector that has connection barrels which require a soldered joint.
00:50 Important to note is that these connectors are supplied with a plastic back shell that attaches to the wiring harness, ensuring the soldered connection will never be placed under any strain.
00:59 The first part of undertaking our soldered joint is examining the type of solder we need to use.
01:04 This is a 60/40 solder with a rosin core.
01:08 So that means it's a 60% tin and 40% lead, and it has a core of flux.
01:13 Now that flux melts and flows out onto the metals that we're soldering, cleaning them, and allows the solder to readily bond with those metals.
01:21 The next stage we need to undertake is to tin the exposed copper conductor section of our wire.
01:27 And this simply means giving it a good coat of solder.
01:31 So we'll go ahead and do that now.
01:40 The next thing we need to do is undertake the same operation but on the terminal of the d-sub nine connector that we're going to connect to.
01:47 So we'll go ahead and do that now.
01:59 With those two items tinned we can go ahead and undertake our solder join.
02:02 Now soldering is one of those operations where it can be very difficult to get everything lined up and it's compounded by the fact that you are dealing with a hot soldering iron so there is an element of safety there.
02:12 What I like to do is prop my soldering iron up and keep it stationary and then bring the items that I'm soldering together, to the soldering iron.
02:20 So I'll go ahead and do that now.
02:23 You'll see when I perform this solder join I'll move the wire and the d-sub nine connector away from the soldering iron once it's complete, but then hold them stationary until the solder solidifies.
02:34 And you need to do this as it will prevent you getting what's called a dry solder join.
02:46 So with that solder connection made, we'll just move our hot soldering iron out of the way.
02:51 And we can have a quick visual inspection.
02:54 What we're looking for here is we want the solder joint to be nice and shiny.
02:59 If you see it dull or looking like it's pitted it means you've probably got a dry solder join and you will need to reheat that and reflow the solder.
03:08 We can perform a small tug test and we see that everything is tight and in place and that's going to be a good solder join.
03:14 Now it's worth mentioning that once you've got all the wires of your wiring harness soldered into their solder barrels, you do want to install the plastic back shell.
03:23 And the way they work is that they grip onto this front flange of the d-sub nine connector and then the wiring harness is strain relieved inside the back shell which means that whenever this plug is installed or withdrawn from its connector, pressure is only applied on the front face here or on the plastic back shell, never on the wiring harness itself.
03:44 So you're not going to strain that solder join.
03:46 That demonstration shows you one of the situations where solder is acceptable in wiring harness construction.
03:51 I do want to stress the point though that it is not a replacement for a mechanical crimp join.
03:56 Particularly when you're splicing multiple wires together.
03:59 When you solder a stranded wire, you're essentially turning it into a solid core wire.
04:04 And solid core wires are exceptionally prone to sustaining vibrational damage from the harsh automotive environment.

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