Pool light wiring question.


Aug 20, 2020
Midwest US
My pool has two 120v spa size lights. There is a J-box (elevated box) for each light.
Each box has three sets of wires. I can understand the 1st box has power, light cord and then line out to the second light. The second box also has 3 sets of wires on it too, and I can't understand what the 3rd set of wires are for. I would guess that they would continue on to another device, but I don't know what it would be. The lights are on a timer and a switch. When off, nothing else turns off, not even a nearby outdoor outlet.
What am I not understanding with the way pool lights are wired?

The whole reason I was looking at this is that the GFCI trips as soon as I turn the lights on. It's done this before after a huge rain, and the J box gets some moisture in it. I want to disconnect a leg of the wiring to see when the GFCI stops tripping, but I need to understand the circuit better. There is a fiber optic light, and an outlet too. The fiber optic light is on a different switch and GFCI, but maybe the power is split off in the J-box?
Any input on this would be appreciated. I'll try to attach some pictures, but they didn't come out too well.
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