The definitive diagnostic procedure I use combines the replacement of the weakest and most vulnerable areas first.
Since 2014 We have offered the new LED dusk-to-dawn control with an 8 second delay for LED. To test you must use opaque black tape and not your finger I do not know why but the control will see through your finger.
If installed after 2014 you can use our 12VAC/DC LED Bulbs. You still need 2 of them to work and they need to be a similar balanced AC LED bulb type we offer on the website.
Incandescent bulbs are subject to water intrusion and power surges. LED bulbs are more forgiving but you may want to seal up the inside top from water dripping onto the bulbs. Bulb brands are another factor, a cheap 1141 can fail faster than a 2000 hr. 1141LL (LL ="Long Life.")
1. Replace both of the bulbs with a set of automotive #1141 bulbs. If one bulb has gone bad the other one will not work because they are in series; 12 volts + 12 volts = 24 volts.
2. Next, bypass the dusk-to-dawn control. If there is still no light you can take the lamp off and hook it directly to the transformer to test the rest of the circuit. A broken wire underground will not short the transformer so you will still have a green light.
If all else fails contact me, I will not give up on making sure your light works as intended.