LED Bulb won’t tighten on quarter turn when replacing the halogen bulbs.

Mopar fixtures, with projector headlights on a 2015 Ram.

 

Are you meaning that the LED bulb is still loose after installing the retainer ring? The bulbs my themselves don't typically twist to tight, there's a retainer ring that holds the bulb in place. Also, some LED bulbs have an adjustable clocking and focal length so that you can match them to your headlight fixtures. Maybe the grub screw for adjusting the bulbs is loose and that's why the bulbs seem loose.

-Rod