[DangeloInspections]

Greg,
You have done all of the correct things. If you have a TIC tester that would help. The post light normally runs off of a 15 amp breaker that is NOT part of the GFCI in the garage.....normally.

Just a few things here. Sometimes the electric eye takes a few minutes to activate after you cover it up. You might not be giving it enough time.

A TIC tester will help, as the first step would be to see if you are getting power to the electric eye before the electric eye. If you are, then you know it is not the underground wire or the breaker. If you are not, then it is one of those two things. Next, wire the electric eye, cover it up, cover it up WELL, then wait a bit and see if you are getting power past the electric eye. if you are, then it must be the wiring of the fixture. Sometimes you might not have a good ground on the fixture. If you are not, it is a bad electric eye.

Lastly, check the fixture wiring. Check the prong at the bottom of the socket, and each socket, (if you have the 3 light type).

Common problems I have found in this project are;
1) Not giving enough time for the electric eye to activate. Sometimes they activate instantly, sometimes they take up to 3-4 minutes.
2) Bad ground.
3) Landscaper cuts the underground wire.
4) Bad socket(s)
5) Blown bulb(s)
6) Defective electric eye

Sounds like you very much know what you are doing....hope this helped a bit. Good luck!

Respectfully, Frank D.