Unplug the light from the power source and allow it to cool for 10 minutes, if it was lit, before attempting to take it down for repairs. Loosen the set screw in the pipe clamp at the top of the instrument with a wrench. Remove the fixture from the pipe or batten and hold it securely while releasing the clip of the safety chain or cable. For chains that use threaded links, release the chain first, then release the clamp.
Set the light on a sturdy, flat work surface. Check the chimney, or round opening, at the front of the fixture to see if it has a lens or if the bulb is visible. If the fixture has a lens, it is a Fresnel. Short fixture with no lens are typically par-style lights. Longer fixtures with a bulb that cannot be clearly seen are ellipsoidals.
Remove the bulb from the lamp. For Fresnels, use a pair of pliers to grasp the ends of the wire spring around the outside edge of the lens. Squeeze the spring ends together and pull out to remove the spring and release the lens. Use a rubber glove to grasp the tube-style bulb. This prevents the oil in your skin from contacting the light socket. Skin oil, if transferred to the new bulb, will cause it to burst when heated. Press in and twist counterclockwise until the bulb stops. Pull it out. For pars, reach in and grasp the round front of the bulb and turn it counterclockwise to remove it. For ellipsoidals, locate the small cylinder sticking off the side of the fixture, perpendicular to the main chimney. Remove the two thumb screws, using pliers if needed. Remove the bulb with gloves.
Replace the bulb. Always wear gloves when installing new bulbs. Press Fresnel and ellipsoidal bulbs in and turn them one half turn clockwise before releasing. Squeeze the wire spring for the Fresnel with pliers and fit the lens in place. Replace the lens in the Fresnel if it is more than slightly cracked. Position the spring and release. Replace the bulb chimney on an ellipsoidal and tighten the thumb screws. Twist a par bulb in as you would for a standard household bulb.
Plug the light into a standard outlet to test it. Changing the bulb will resolve most problems. Replace the light. Fasten the safety chain or cable first to support it in case of a fall, then fit the clamp around the pipe and tighten it snugly with a wrench. Plug the instrument back in once it is safely installed.
Unplug the light and cut the cord just above the plug if the wires appear loose or frayed. Strip the ends of the three wires in the cable by fitting each into the correct hole in the wire stripper jaws and closing the tool firmly to cut the casing. Pull toward the end of the wire. Remove the two screws in the end of the replacement plug and separate the cover from the plug. Fit the wire through the hole in the top of the cover. Loosen the screws on the plug. Fit the black wire to the screw marked with a "+" sign and the white wire to the screw with the "-" sign. Fit the green ground wire to the green screw. Tighten all screws, refit the cover over the plug and tighten the screws holding it on. Plug in the lamp and test it.