Why aren't my in-ground lights receiving power?
Only 1 out of 6 of them light up.


So we know at least one of them is working. Odds are that fixture is the first in the string of the lighting circuit. I am assuming they are all on the same circuit. I am also assuming there is a photocell or timer that turns them on and off. Is there a lighting contactor involved? If not then you need to investigate the one that is working and see if there is a loose or corroded connection there. 

If everything looks fine then you need to determine the route of the underground connections. Then by disconnecting the wires at the one light that is working and separate the line side (the one that is hot) from your load side to the next fixture. Twist the load side together. Using a continuity tester or ohmmeter go to the next fixture in the string and see if you can get a ring or a reading. If you can't get continuity then you have a break in the underground connection and it must be replaced or repaired. So make sure all splices are clean and corrosion free.

The hard part is trying to determine the route of the underground conductors. It's usually in some form of a loop. We are taught to use the shortest route possible, if that helps. If you can't figure it out then you will need to continue disconnecting fixtures and ringing between the fixtures to determine the route. 

Remember you will be kneeling on damp ground so once you find the line side of the first fixture. Be sure and turn your power off to avoid shock.

Stay safe and good luck.