GFCI outlet for pool, spa lights keeps tripping

[SemperFly]

Hello Everyone.

I have an issue with the gfci outlet, that also protects my pool/spa lights, instantly tripping when either side of the light switch is closed. I've checked the wiring at at the switch, the gfci outlet, and the junction box for the lights, and it all looked OK. I replaced both the switch and the gfci outlet. And, finally, I tried isolating the pool light and spa light by disconnecting them individually in the junction box, which also served to reset all of the connections in the box. The only thing I can think of that is left, is to replace the lights themselves, but I thought the odds would be low that both lights are failed, and I'd like avoid dropping $1000-1500 on light fixtures as a troubleshooting measure. The pool is 35 years old, and the lights are of an unknown age, but I inherited them 7 years ago and the issue was present then. I've only now been inspired enough to try to figure it out.

Pool Light: American Products R500BC, R-40 in a CN-5 housing
Spa Light: American Products R400BCL, R-40 in a CN-5 housing

I have no automation. Here are some pics of my setup.
Note: the blue wire on the gfci outlet is the hot wire from the main CB panel.


Sparkys...please help!!

Thanks

 

[Rocket J Squirrel]

finally, I tried isolating the pool light and spa light by disconnecting them individually in the junction box, which also served to reset all of the connections in the box. The only thing I can think of that is left, is to replace the lights themselves, but I thought the odds would be low that both lights are failed,

I don't understand "which also served to reset all of the connections in the box". What does it mean to reset a connection in a j-box?

What was the result when you had each light connected individually? The GFCI still tripped when only one light was wired?

 

[Ahultin]

If you individually bypass the switch (red to yellow) does the gfci switch on both lights or only on? With the switch connected, but the yellow's disconnected at the junction box does the gfci trip?
Have you tried a continuity test on all of the wiring?
Does the gfci trip if you remove the bulbs from the fixtures?

 

[SemperFly]

I don't understand "which also served to reset all of the connections in the box". What does it mean to reset a connection in a j-box?

What was the result when you had each light connected individually? The GFCI still tripped when only one light was wired?

I just meant that I had disconnected/reconnected every connection in the j-box, eliminating the possibility of any bad/loose connections.

Yes, when wired individually, the gfci still tripped instantly when the switch was closed for the respective light.

 

[SemperFly]

If you individually bypass the switch (red to yellow) does the gfci switch on both lights or only on? With the switch connected, but the yellow's disconnected at the junction box does the gfci trip?
Have you tried a continuity test on all of the wiring?
Does the gfci trip if you remove the bulbs from the fixtures?

I replaced the switch with a new one, but haven't tried bypassing the switch altogether. I will try that and report back.
Do you mean, disconnect both lights yellow/black, but leaving the commons connected? I haven't tried that combination.
I haven't done a continuity check of the wiring.
I was planning to remove the light fixtures today and open them up to test them with a regular floodlight bulb.