According to John :
"DoN. Nichols" wrote:

[ ... ]

And the *good* crimped terminals -- the pre-insulated ones with
a P.I.D.G. crimper will collapse the rear of the insulation sleeve to
grip the insulation, thus reducing the flex at the terminal. In
particular, the AMP terminals for the P.I.D.G. (Pre Insulated Diamond
Grip) have a sleeve of metal shim stock around the terminal barrel and
inside the insulation, with the last bit folded back to the edge points
towards the terminal. This bites into the insulation to grip it more
firmly than possible by just collapsing the plastic insulation to form a
grip.

[ ... ]

In my experience, the biggest problem with failure of crimped terminals
is that the installer did not use a proper crimping device, or the unit
was not calibrated with a go no go gauge. The cheap stamped out
crimping might be ok for household use but they spring and don't do a
secure crimp.

They are -- at best -- emergency field repair tools, and the
crimp should be re-done with a proper tool when you are back home (or
wherever the proper tool is).

A good T & B forged crimping tool is a lot better way to
go than the stamped ones if you can find one used in good shape. The
best crimpers are the ones that have a racheting system that will not
release until the proper pressure is put on the crimped terminal,

This describes the AMP tools which I was suggesting upthread.

but
these crimping tools must be checked periodicly with a go no/go gauge.
Overcrimping is as bad as under crimped terminal. Overcrimping cuts the
wire and although the terminal looks like a good crimp a number of wires
are cut and the terminal is held on mostly by the insulation. On the
high end crimping tools, there are identification marks that are on the
crimper that leave the same mark on the crimped terminal so the
inspector can tell if the terminal was crimped with the right tool.

Right -- red (22-16 ga) is one dot, blue (16-14 ga) is two dots,
yellow (12-10 ga) is back to one dot, but there is sufficient difference
in size so there is no way that a terminal crimped with one size of one
dot tool instead of the proper one dot tool would pass the simplest
visual inspection.

Once you get past 10 ga, the rest (all hydraulic in my set)
emboss the actual gauge number in the insulation barrel, because it is
now big enough to read easily.

Enjoy,
DoN.
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