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Re: wiring techniques

Subject: Re: wiring techniques
Date: Wed, 25 Jun 1997 23:38:06 -0400 (EDT)
In a message dated 97-06-25 14:42:32 EDT, (EMILY COWEN)

> Soldered spade connections are subject to vibration failure because the
>  solder wicks past the end of the spade connecter into the wire.  The
>  area where the solder ends is a stress point, and vibration will cause
>  the wire strands to work harden and fracture inside the insulation where
>  you can't see it.  But that point WILL get hot before it eventually


There is a lot of contention over this point. Some people swear by soldered
joints, and others won't use them at all. My opinion is that EITHER soldered
or crimped joints are perfectly OK, provided they are made correctly, and the
rest of the wiring installation is correct.

Vibration is a problem only if there is a sufficient length of unsupported
wire, which is allowed to move with respect to the connection. In other
words, it is the flexing of the wire that causes the wire to work harden and
break. You are absolutly right when you say that the solder wicks up the wire
for a short length, causing it to be stiff. The point where the stiff portion
of the wire meets the flexible portion is where the problem is. This is also
a problem with crimped joints. The joint itself is very stiff, exactly like
the soldered joint. If the wire is allowed to flex, it will break just the
same as it would for a soldered joint. The one real disadvantage of the
solder joint is that the extra length of stiffening makes it harder to route
the wire, as the bend radius is too large.

Rule # 1 Never allow the connector to be the support for any appreciable
length of wire. 

The wire must be supported so there is no movement relative to the
connection. This is true even if you are wiring bewteen two components that
must move with respect to each other. The wire must be supported so there is
no movement AT THE TERMINAL!

Rule # 2 A GOOD X type connection is better than a POOR Y type connection.
Insert your choice for X and Y.

If I could get a good crimping tool, and good crimping terminals, I would
never make another soldered connection. The joint made by the factory, using
automated crimping tools, is unbeatable. The tools that are available for the
average person are only OK at best, and terrible if not used properly. If you
notice, the jaws on most crimping tools do not close completely. If you use
the correct size terminal, the correct size wire, and the correct crimping
tool opening, and squeeze till the tool stops, you will produce a good crimp.
Otherwise, it is possible to crimp too hard, and weaken the wire, or not hard
enough, and get a weak connection. The thing that bothers me the most about
standard crimpimng tools is that they crimp "across" the wire. This places a
great deal of stress over a very small area, making it very susceptable to
breaking due to flex stressing.

>  > discussing resistance, not structural strength.  Soldering beats 
>  > pigtailing in that respect, hands down.
>  Actually, in the real world, it doesn't.  It's entirely possible to have
>  a cold solder joint that LOOKS great, and functions erratically, with
>  varying degrees of resistance as the joint heats up and cools down.
>  Ever had a tv/radio/sterio that you had to pound on to get working
>  properly?  Chances are you're living with a cold solder joint!!

You're probably all too right about that, Kirk. I suspect that many don't
know how to make a realy good solder joint.

Rule # 3 The material you are soldering must be hot enough to melt the
solder. It isn't good enough that the soldering iron melts the solder.

If you touch the solder to the iron till it melts, and let it flow around the
wire, it will produce a glob, and the solder will not stick to the wire. It
may look like it did, but it didn't. Unless the solder flows when touched to
the wire, but not touching the iron, the wire isn't hot enough.
Unfortunately, if you hold the solder to the wire, and wait til it is hot
enough, the lenght of time that takes may melt the insulation. A good
technique to use is to melt a glob of solder on the iron, where it touches
the connection, and let it flow around the connector. When the connector and
the wire are hot enough to melt the solder, you will see the blob of solder
flow and smooth out. At this time, the joint is hot enough to complete the
soldering by adding more solder. The glob of molten solder acts as a heat
sink, transfering the heat to the joint better than just the contact of the
tip of the iron. When a solder connection is made well, the solder flows
smoothly, and basically becomes one with the joint. If there is any
abruptness in the solder flow, it is probably a cold joint. In other words,
if it looks like the solder is just sticking on, it probably is just sticking
on. A little practice with some scrap wire and connectors will make this all

Rule # 4 Use the right heat range soldering iron/gun. 

Too big is better than too small for our usage. A hot iron will get the joint
to the proper temperature quickly, so you can make the connection and get
away before the heat has had time to flow to adjacent areas, or up the wire.
An iron that is too small will take so long to get the joint hot enough that
the wire will be hot for an appreciable length, and might even damage the
insulation before you can finish. It is also helpful to use low temperature

Of course, you already know all this, but it might be helpful for others on
the list. Anything you would like to add? Did I get it right?

Dan Masters,
Alcoa, TN

'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74

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