Inground Pool Light wiring 1968 pool.

[ESA1178]

Hi all!

As you can see by the photo I have a junction box that houses a bunch of wiring. I am assuming that this is to facilitate the pool light and something else in the past. This is also where the diving board sat.
There are 3 conduits. The center probably goes to the light, since it is B/W/G.
The others I am not sure about. Obviously one has to be a source. They are both BL/W/Y/B/G.
I just had the pool re plastered and cement deck partly replaced. During the removal of the old cement, it was found that the old wiring was encased in rusting black iron (go figure). I told the guys to remove it. Now I am going to cut a 3 inch wide section of the old cement, leading from this box to the bedding area (about 6 feet.) Then I am going lay conduit to the main panel. My questions is, what gauge wire should I be using to pigtail with the B/W/G? And also what breaker/fuse? Since this would be dedicated fuse/breaker, I assume on the low end.

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Many thanks for all your help guys/gals.. have a great summer!