I remember, about 10 years ago, being challenged by a bus mechanic to come up with a way to stop the wires for all the auxiliary lights from corroding. He spent so much time tracing wiring back to its source, replacing bulb housings, and weather sealing, that he thought there must be a better way.
dont know if mine is the best or not well, Im sure its not, but here goes:
Have a centrally generated source of UV light that is easy to access. Thisd probably look like a mirrored chamber with a fluorescent bulb inside quite small.
On the sides of the chamber would be small screw-in ports for the fiber and optical switches. From these ports, fiber would run to wherever the light is needed and enter a mirrored housing through a diffuser lens.
The part of the housing you see from the outside would be formed from a clear lens, coated on the inside with a substance that glows in the presence of UV light. Pick your color.
Brightness and switching is controlled back at the ports on the UV generator.
Nothing electrical, all plastic, so no corrosion.
If the big bulb dies, then they all go out so have a second bulb for redundancy.
Another version of this idea would use white light as a central source, with tinted lenses at the output side. Simple, but not as power efficient.