How to Replace an Underwater Pool Light

Watts Happening: Advances in Pool Lighting
by Mark Garcia December 13, 2013

underwater pool lightThere's a question I'm commonly asked. "Can I just replace the light fixture, and use the old cord?" No, not possible to do, as the cord is not removable from a pool light. I was even asked recently if the epoxy in the bottom of the light could be dug out, the socket replaced, and new epoxy poured back in? Also not possible, or at least not recommended.

So, you need a new pool light? You may be replacing the entire pool light if you have corrosion eating a hole through the lamp fixture body, more common in the very old copper lights, or when the socket or internal cord has shorted out, and the power delivered to the socket is less than it needs to be to light the bulb. Or, you may be changing the complete pool light when you want to upgrade to LED color pool lighting. This is more commonly the reason for replacing the entire underwater lamp.

How to Buy a Replacement Pool Light

There are three things to keep in mind - very specific things, so that you buy the correct pool light.

Voltage: Number one is voltage. Most swimming pools in the U.S. are using 120 volt lights (110, 120, 130 - same thing). There are a few places, such as Montgomery county, in Maryland, that are required to use 12V pool lighting. The light fixtures look identical, but you should notice it labeled as a 12V pool light. 12V pool lights also make use of a transformer, in between the breaker box and the junction box. This is a transformer by Intermatic, shown here, which is usually mounted on a wall, near the breaker panel for the pool equipment. The transformer sits in between the breakers and the junction box, for 12V pool light system. Again, most pool lights are systems are 120 volts, but check to be sure.

pool light with cordCord Length: The second thing to be careful of, is to make sure that you buy a pool light with a cord that is long enough to reach the junction box, plus 3 or 4 feet of cord coiled up inside the niche. The extra cord is important so that you can have enough slack to pull the light up on deck for bulb replacement or other maintenance tasks. Pool lights are commonly available in 15 ft., 30 ft., 50 ft., and 100 ft. cord lengths. Buy the one with a cord length that is longer than you need. The extra pool light cord that you cut off makes a nice extension cord, with a couple of plug ends.

pool light nicheNiche Size: The pool light niche is the bucket turned sideways that the pool light fits into. There is no standard size, and they all vary by an inch or so. Hayward, Pentair, Sta-Rite - they all have different diameter light niches, which fit different sized pool lights. It is possible to get a different sized light to screw into the retaining hole, at 12 o'clock, but if you want a proper fitting pool light, make sure you are replacing the pool light with the same exact pool light. For LED pool lights, Jandy, Pentair and Hayward all make their own LED pool lights, designed to fit their light niches.


How to Install a Replacement Pool Light

This information is for qualified, careful and sober peopleCAUTION:  this procedure should be performed by a qualified person, working with electrical wiring can be hazardous. You will need to use an electrical test meter to verify that the power is off before opening the junction box. Read all instructions and read all of the precautions that come with your new pool light before attempting to install a pool light.image credit:

Step 1: Read the owner's manual for your pool light for specific instructions and precautions. After that, start by turning off the power at the breaker panel for the pool equipment. The pool light breaker is usually a 15 amp GFI, with a test button, but to be sure, shut all of the breakers off. This is a good time to test the GFI test button on the breaker, to be sure that it pops when you push it. If you have to leave the job for a few minutes or a few days, always recheck the breakers before starting work again.

Step 2: With the power off, locate the light junction box - usually directly behind the pool light, off the pool deck, raised about 12 inches above the water level. In cases (like outs) where there is more than one junction box,, and they are both mounted back by the equipment or next to each, you may have to guess at which j-box is the j-box for which pool light. Choose the one that is on the opposite side as the pool lights. That is, when facing the pool, the pool light that is one the right, will run to the j-box on your left, as you turn around to face both junction boxes. But not always :-). A better way to find out is to wiggle and pull the pool light a little, with a helper looking, or feeling for movement made on the other end.

Older pools with underwater lights may have the junction box located beneath the rear of the diving board, and on very old pools, it may be located in the pool deck, beneath a steel plate. If it is located in the pool deck, you may be required to bring to pool lighting up to code, and relocate the junction box to a new and higher location. Remove the junction box lid and unscrew the wire nuts joining the wires from the breaker to the wires from the pool light. Take note that there are two black wires, two white wires and two. If the wires coming from the breaker box are any other color schema than this, be sure to label the ground, the neutral and power lines. Use a test meter to confirm that the power is off before proceeding.

Step 3: Remove the pool light from the light niche and cut the cord just behind the pool light, so that the old lamp is disconnected from the cord. If the pool is drained, inspect visually and close-up where the cord leaves the light niche. If there is a mound of pool putty, or even worse, silicone, you need to remove this first with a flathead screwdriver or other tools. If your pool is not drained, you'll have to inspect for silicone or pool putty by hand or underwater with a mask. If you reach down deep into the niche, you can feel the edge of the conduit connector. You want to feel some movement or play in the cord, inside of the conduit. If you can't move the cord at all side to side or in and out, then you may need to lower the water and remove anything that would prevent you from easily pulling the new cord through out of the niche and into the conduit.

tape the ends of the cordsTake the new light and stretch it out, to the other end of the pool, working out the coils, so the cord is relatively straight. Use wire snips to cut off the stripped wires from the end of the new cord. Use a cleaning solution to clean the end of the old cord if necessary, to remove any slimy gunk and dirt. With 3 pieces of 6 inch lengths of duct tape, join the end of the old cord to the end of the new cord, overlapping each piece in the opposite direction of the piece beneath. It's very important to tape the ends together solidly so they won't come apart. You also want the tape joint to be thin, if it's too bulky you may have trouble pulling the cord through the conduit. If your tape connection fails, and you pull out only the old cord, you will need to use a fish tape, pushed from the junction box towards the pool light. Connect the fish tape to the new light, and pull the new cord through. Or you can use this method from the start, if you like.

Step 4: Return to the junction box and remove the saddle clamp that is holding the pool light cord in place. Grab the light cord firmly at the junction box, and pull it straight up. You may need a helper at this point, leaning over the pool, helping to push the new light cord into the conduit, and helping to keep the cord from coiling up again and getting stuck at the point where the conduit connects to the upper rear of the light niche. Keep pulling the cord out of the conduit, and eventually you will pull up the tape joint. Keep pulling until the new cord is all the way pulled through, leaving 3-4 feet of cord, or enough cord in the pool to pull the light up onto the pool deck for future service.

Step 5: Replace the saddle clamp that holds the pool light cord in place at the junction box, and strip the light cord casing down to just above this point with a razor knife. Cut vertically through the sheath, and then around the diameter of the cord, being careful not to cut into the 3 wires. You can gather up and cut off the white insulation material. Using wire strippers, cut the 3 wires to an appropriate length, about 4-6 inches, and then strip off the last half inch or so of insulation. Connect the green wire to the green ground screw, or into the green jumper wire attached to the ground screw, and then wire nut the two other wires, black to black, and white to white. Now you are ready to test your new pool light. Only test it with the lamp submerged in water, it needs the water to cool, or the lens will burst within 1 minutes time. Turn on the breakers and flip the switch.

closing up the junction boxMake certain that the wire nuts are tightly twisting both bare copper wires of about 1/2" together, and use electrical tape around the open bottom of the wire nut, for extra sealing protection. Twist the wire groups together loosely, and firmly coil them around in a large oval shape and then work the top of the junction box back on.

With the gasket in place, push the lid down firmly so you can get the too tiny screws into the too tiny holes. Use all 4 screws to secure it tightly.


Step 6: Coil up the excess cord around the new pool lamp and insert the lamp into the niche, by first attaching the tab at 6 o'clock, and then tightening the screw at 12 o'clock.

Pool Light Problems and Solutions

If the pool light does not come on when you test it, open the junction box and check with the test meter probes, one on each the white and one on the black wire. You don't need to remove the wire caps, if you push the leads up into the bottom of the wire nut firmly. If there is power, it may mean that the bulb inside is loose or broken. If your pool starts leaking after you replaced the pool light, you can take a guess that the leak is coming from the conduit, especially if there was a mound of pool putty, or a light cord stopper being used on the old cord.

You don't need to drain the pool water down to replace a pool light, but it can be helpful, otherwise your helper will be getting very wet, helping to push the cable through. Pushing is sometimes as important as pulling to get the new cord through the conduit.

CAUTION:  this procedure should be performed by a qualified person, one familiar with working with electricity. You will need to use an electrical test meter to verify that the power is off before opening the junction box. Power must stay off the entire time. Read all instructions and read all of the precautions that come with your new pool light before attempting to replace a pool light.


Thanks for Reading!
Mark Garcia