Electrical solderless or soldered connectors

threewood said
wouldn't a crimped connector create the same issue?

yes

Mattax said
Most of the terminals on the car had a second crimp that holds the insulation. This provides support so wire movement is not concentrated at the end of the flexible portion of the wire.

threewood said
And I have to believe vibration in the middle of a wire that is shrink wrapped is not going to flex to failure.

That depends on how its supported and the type of heat shrink.