I have two headlights on the front of my boat. Both of them wired up the exact same with same 12g wire both have their own wires that run all the way back to the battery. When I installed them years ago was told to break the negative with the switch. I had no issue until last year one light burned out on me. Thought it may have been bad considering it was 5 years old. Installed two new lights Friday, went fishing the same light burnt out about half way through the night. It slowly dimmed down then went out. I noticed the lens kind of looks smokey or milky

Does anyone have any idea what may have caused this to all of a sudden start doing this?