[TR] Soldered Wire Connections in Cars

[Randall]

Hmmm, seems like this didn't make it through before.  Apologies if it comes
through twice, but here's a shorter version :
 
> Is this urban myth, or is there truth to it?

I believe there is some truth to it.  Not that soldered joints should not be
used on cars; but that they can have problems if used incorrectly.

The issue is that if copper is flexed beyond it's yield point (which is
relatively low), it will work harden, crack and break.  A bare solder joint
leaves a sharp boundary between the stronger joint and the wire itself, such
that if the body of the wire moves due to vibration, it will flex right at
the transition from the solder, and eventually break at that point.

This problem is real, I've seen it happen.

Crimped joints, in theory, don't have the problem as much, because they
provide a gradual transition from the tightly clamped portion of the wire,
to the totally unclamped portion.  But in my experience, they suffer from
other shortcomings, primarily that of the crimp itself losing clamping
force, which eventually allows the wire to not make good, gas-tight contact.
The result is oxidation of the copper, which leads to a poor connection.
There are also problems with getting the clamping force just right to begin
with; as even the expensive calibrated ratcheting crimpers don't always get
it right (and most people don't use them or keep them calibrated).

> The protocol for joining wires among the motorcycle
> groups I knew (online and in-person) was to solder and protect with
> heat-shrink wrapping around the joint.

Heat-shrink is a good way of helping ensure that the wire does not flex at
the surface of the solder joint.

My favorite technique for terminating vehicle wires is to use a crimp-style
terminal (ring, spade, quick connect, whatever is appropriate).  I either
use un-insulated terminals, or cut the plastic insulation off; then crimp it
to the wire.  Then I solder the wire to the terminal, beyond the crimped
area, being careful not to let the solder wick all the way back through the
crimp.  Then I add heat shrink tubing (if possible) that covers from the
crimped area all the way back onto the stripped-back insulation.  This both
adds strain relief and helps protect the wire and crimped joint from air and
water.

In the nearly 30 years that I've been doing joints this way, I've never seen
one fail.  But I have seen lots of both solder-only and crimp-only joints
fail (including ones I've done).

I used to work for a company that installed computer systems onboard seismic
survey ships.  We had literally hundreds of wire connections to other ship's
systems, so I saw lots of bad joints, including crimp joints made by
professionals with those calibrated, ratcheting crimpers.  Properly
supported solder joints did better at least in that environment (and IMO).

Since the usual rule was that I couldn't go home until everything worked, I
got real interested in those joints <G>

Randall