I do not know the extent of the work or whether a permit was required. If in fact a GFCI was installed, it would have not been able to be reset. If they had worked on the light they would have to install a GFCI in event it was not present. I agree, with the age of LED low voltage lights and fiber optics, line voltage lighting in pools and ponds should be a thing of the past. I would not install one.
