Hello,
Thanks for the post, normally the unit is supposed to be tight to prevent moisture from getting inside the end cap. You may want to try a silicon lubricant to help the end cap turn on the bulb easier. That usually will help, just make sure that you use the lubricant sparingly and wipe the bulb clean before you light the bulbs.
If you continue to have trouble please feel free contact our Customer Care Center at 1.800.566.3474
Best regards,
Walter
Marine Depot Customer Service