Faston Connectors on Coil packs

Faston connectors, if quality units from a US manufacturer, are very reliable and handle vibration well.  They generally don’t fail unless they have been installed and removed many times or installed improperly.  If misaligned and forced onto the spade at an angle, the ears can be sprung open a little and they won’t hold well.  Generally, this is easily corrected by slightly squeezing the connector using Vise-Grips.  Pliers are trickier as you can easily squeeze the contacts completely closed making them very hard to install.  Vise-grips allow you to squeeze a controlled amount and close the contacts just enough to tightly hold onto the spade terminal again.

Not sure who suggested soldering, but that is very bad advice for this application.  Solder will stiffen the wire and create a stress concentration at the end of the solder wick that will break the wire from vibration.  Much better to either fix the faston with vise-grips or, if the connector is damaged beyond repair, cut it off and crimp on a new one.