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How to Install Mercury Vapor Outdoor Lights

Mark Morris

Mercury vapor lights are designed to be long lasting and can produce a lot of light from standard voltage. The fixture itself is similar to standard light fixtures with a three-wire lead and a large Edison-style twist-in socket.

It's best to use plastic wire nuts to make your electrical connections.

You will need to have a professional electrician make the main connection to the breaker box — and run one cable to the junction box for the switch and one for the light — to ensure safety and meet building code requirements.

  1. Locate the breaker connected to the circuit your new light will be on and turn it off.

  2. Remove the cover from the switch junction box with the screwdriver and pull the wires out of the box. Remove the wire nuts from the ends of the three wires from the breaker box and the three wires from the light junction box. Match the white and green wires up to each other and twist a wire nut onto each pair, turning it clockwise to tighten.

  3. Attach the black wire from the breaker box cable to the top screw of the GCI light switch. GCI switches must be installed on outdoor applications. The switch features a circuit interrupter that breaks the connection in case of a short, including water in the switch. Wrap the wire around the screw and turn the screw clockwise to tighten it. Attach the black wire from the light cable to the bottom screw in the same way.

  4. Fit the switch into the junction box and install the top and bottom mounting screws through the tabs on the switch into the threaded holes in the junction box. Fit the hinged cover switch plate onto the box, making sure the rubber gasket lines up with the edges of the junction box.

  5. Remove the cover from the light junction box with the screwdriver. Pull the wires out and remove the wire nuts from the ends of the wires. Match the cable wires in the junction box to the wire leads on the back of the light fixture — white to white, black to black and green to green. Fit each pair with a wire nut and turn them clockwise to tighten.

  6. Install the mounting bolts in the junction box. They will poke out from the rear of the tabs in two corners of the box. Fit them into the box and push the threaded ends back toward you until the heads are against the back of the tabs. Fit the holes in the base plate of the light fixture over the bolts. Put a rubber washer over each bolt. Thread a nut onto each bolt and tighten them with pliers.

  7. Turn on the breaker and open the cover to access the light switch. Turn on the power switch to the light and wait for the bulb to heat up to full strength.