Be very careful when working with electricity and water. Make sure to follow every possible safety precaution and to turn off the power at the main circuit breaker, and mark it to be left off while you are working.
If, after turning on the pool light switch, the GFCI trips (see page 1 on What to do When Your Swimming Pool Lights Don't Work), the most likely cause is water inside your light fixture.

If the GFCI doesn't trip and the light is off, you probably have a burned-out bulb. In either case, you must now proceed to pulling your light fixture out of the pool:

1. First make sure that the breaker, GFCI, and pool light switch are all off. It is a good idea to put a piece of tape over the breaker to help keep someone from turning it back on.
2. Now, to get the light fixture out, you will need to unscrew the small pilot screw that holds the fixture in. This screw is usually a Phillips screw (top looks like a "+") and is at the top of the fixture, closest to the light lens. Do not confuse this screw with the screws that circle the light and hold the light ring on a vinyl liner pool.
3. After loosening this screw, you should be able to bring the light fixture out of its niche and up out of the water and onto the deck. Note: Some lights are held in by a clip in which case there is no pilot screw and you will need to use a screw driver to pry it out. Make sure yours is this type before prying or you may break the fixture or niche.

1. Sometimes the cord may not be long enough for the light to reach the deck. After questioning the ancestry of the idiot who installed the light, you will need to go to the junction box that the light cord is connected to. This junction box could be inside your dive stand. You will need to disconnect the light cord at the junction box and be sure to attach a piece of wire or strong string to allow you to pull the cord back when you are finished. Note: Pool lights are designed to have water inside the niche that holds the light fixture. This helps cool the light and allows you to pull out the fixture with water still in the pool.
2. Now that you have the fixture on the deck, you can open it up. You will find one of two types of fixtures. One type has many screws around the back of the fixture rim; the other has one screw that tightens a band clamp that holds the fixture together. After removing the clamp or screws, you may need to pry open the fixture. Be careful not to break the lens when you do this.
3. With the fixture now open, you may see the water that was causing the GFCI to trip, in which case you will need to dry out the inside of the fixture. You can use a towel and/or hairdryer for this. You should remove the bulb and dry the connections thoroughly. Note: Halogen bulbs should not be touched directly with your hands. The oils from your skin can reduce the bulb life.
4. After drying thoroughly, put the bulb back in and try turning on the light for a few seconds. Do not leave the light on for more than a few seconds. Remember, it is supposed to be water cooled. At this point, you may find the bulb is burned out and needs replacing.
5. If the bulb is burned out, replace it and try to turn it on for a few seconds to test it.
6. If it works, you can proceed with reassembling the light fixture. Be sure that the breaker, GFCI, and pool light switch are all off. NOTE: You should always replace the light gasket because the high temperatures of the light can make the gasket form to the fixture, and you cannot put it back exactly the same way. Be sure to tighten the screws evenly on the fixture to prevent it from warping and not sealing properly. For the clamp type, it is a good idea to tap around the ring as you tighten to even out the pressure around the ring.
7. Hold the fixture underwater and look for bubbles coming from around the gasket. If this happens, you may need to reopen the fixture, dry it out, and reassemble.
8. Next, put the fixture back into the niche. For deep fixture lights, you can wrap the cord around the fixture. There is a notch on the bottom of the fixture that catches on the bottom of the niche. Now, screw in the pilot screw or snap in the clipable type.
9. If you who had to disconnect the cord at the junction box, you will need to pull the cord back as you put in the fixture. Do not splice an extension to your cord. The conduit that the cord goes through has water in it and the splice will be underwater. If you wish to correct the short cord problem, you will have to replace the whole light fixture. You cannot install a longer cord because it is sealed during the manufacturing process.
10. Turn your breaker and the GFCI back on and check your light. You should be ready for your night swim!