New homeowner here. This weekend I replaced the light fixture on the post in the front yard. When the lights would not illuminate, I checked a small electrical box on the front of the house and discovered some disconnected wires. After connecting the wires, the light worked for about 8 hours until it tripped a GFCI(no breakers) and shut off. I pressed the reset button about 10 time before it stayed in place. The light stayed on for several more hours before the GFCI tripped again. I then replaced the GFCI and encountered the same results hours later. Any suggestions?
I agree with KBsparky a good chance you may have bad spot on the cable or a nick somewhere along the way.
So unforetally you have to bury a new cable to slove the issue and with 15 or 20 amp 120 volt circuit with GFCI you can buried them 12 inch deep that is the only part you can do this otherwise any other size or voltage it have to be at least 24 for UF or Direct bural cable or 18 inch in conduit.
Also while ya digging up a new cable why not go with XX-3 cable so you have one on switched circuit for your luminaire while second part you can used for receptecale at the luminaire location.