Our 'new to us' boat has two underwater lights - seen during survey haul out - and easily found when looking at the transom from inside the boat.
The lights appear to not work (turning rocker on helm on and off while dark outside).
Did not see excessive growth covering the lights during the haul out. So don't believe they're simply fouled.
My next step (next time I'm at the boat) will be to test voltage to the lights by removing the screw on 'cap' (#1 below) with wiring leading to the light (I don't believe this breaks a water tight boundary, but will certainly have spill protection ready and also be ready to screw it back on quickly.
If voltage check is ok, my next trouble shooting effort would be to check the lights themselves to ensure there's not an open in the filament (not sure if these are filament or LED).
It certainly appears that the hardware is set up to allow access to the light from inside the boat (#2 below). NOT SURE IF THIS BREAKS THE WATER TIGHT BOUNDARY or if the lens that covers the light is the boundary (which makes more sense in my mind since you don't want to get the bulb wet).
So question for those who have replaced uw lights before - can I do it wet, or need to wait for next time I'm on the hard?