Nearly everybody likes to use LEDs in their games. They run cool, save energy, they don't melt your inserts when the transistor sticks on and they can give a color boost to old, faded inserts.
Classic Bally and Sterns have some well known problems using LEDs. LEDs use 1/10 the power, so they often flicker by not drawing enough current and many of those bulb sockets are long past their useful age. Either the internal spring has broken, or the assembly crimp has lost it's tension - causing intermittent lamp illumination.
Some past fixes were to add a resistor to each socket to reduce flicker (very labor intensive), get a "resistor board kit", or a whole new Lamp Board with modern design.
https://pinside.com/pinball/forum/topic/classic-ballystern-led-adapter-kit-review
As far as the loose sockets, you could solder the ground lead to the socket tit, or buy a new socket for $1.50
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