Things You'll Need
Mercury vapor light ballast or photocell
Ladder (if necessary)
According to the United States Government Printing Office, the Energy Policy Act of 2005 prohibited the manufacture and importation of mercury vapor light ballasts after January 1, 2008. Despite the mandate, there are plenty of old outdoor mercury vapor lights still in use in the United States. Ballasts and photocells can still be found on the dusty back shelves of some hardware stores. Online lighting supply dealers also carry a few ballasts manufactured prior to 2008. When the ballast or photocell in your outdoor mercury vapor light fails, you can still repair it if you can find the parts.
Turn off the electricity to the outdoor light. If the light is on a breaker, turn the breaker off. Place a ladder against the pole and secure it so that it does not shift. Ask someone to hold the ladder for you.
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Loosen the screws on the ballast cover and remove the cover. Unscrew the bulb and place it in a safe place.
Remove the screws or wing-nuts that secure the ballast wiring inside the light. Turn the ballast counter-clockwise and remove it from the fixture. Screw the new ballast into place and replace the screws to secure the wiring connections.
Unplug the photocell. Twist the photocell counter-clockwise and then unplug the cell from the fixture. Insert a new photocell. Twist it clockwise until it stops.
Retrieve the bulb and screw it back into the fixture. Replace the ballast cover and tighten the screws. Turn on the electricity. Cover the photocell with your hand to block the light and force the light to turn on to test the repair.
Buy more than one ballast and photocell when you find a dealer that still carries them.
If you must use a ladder to reach the light, use a carpenter's belt to hold tools, parts and screws while you are repairing the light to avoid climbing up and down the ladder.
Never climb a ladder that is not properly aligned and secured. Have a friend secure the bottom of the ladder to prevent it from shifting or falling.
Never attempt to repair an electrical device without first determining that the electricity is turned off. Serious burns or death from electrocution may result.