While I agree with always Soldering any Coil Lug/Wire in general.
I have NEVER had 1 single issue with ANY of our Bally/Williams Pins that had them installed from the factory.
IIRC they started with NGG through the Pin 2K Games (NGG, CP, MB, CC, RFM & SWE1) - every Coil in those Games used .125 &/or .250 Molex Quick Disconnects & I've never (knock on wood) had a Coil QD issue (coming loose or a or power problem) with any of those Games.
Since only six Pins B/W made this way and not as old as many Games made before them so a few more years may tell a different story but so far so good.

Over the years I've purchased 2 Games from different operators that had put 3-M Bullet type QD in line on the Wiring Harnesses on every single Coil & PF Mech/Toy with no ill effects that I've ever noticed.
A Fun House & an STTNG, I REALLY expected STTNG (with all the under PF Mechs) to have issues but none to date & I'm going on 3 years of owning this one.

Kim

www.KimballsPinballs.com