Learn and use some electrician’s skills to wire up a sample circuit with a junction box, switch, and light, then test your system using a safe amount of DC voltage.
Source a string of small incandescent Christmas lights at a thrift store to take apart with your wire cutters, leaving about 3” of wires attached to the bulb. Test with a battery or multimeter to make sure the bulb works before you wire it into the circuit. See “extension challenges” below for how to build this circuit with LEDs.
Check out our Tool Tutorials for more instruction on how to use multimeters, wire strippers, and Linesman’s pliers.
Explore Related Trades Careers: Construction Electrician, Industrial Electrician, Marine Service Technician
Source a string of small incandescent Christmas lights at a thrift store to take apart with your wire cutters, leaving about 3” of wires attached to the bulb. Test with a battery or multimeter to make sure the bulb works before you wire it into the circuit. See “extension challenges” below for how to build this circuit with LEDs.
Check out our Tool Tutorials for more instruction on how to use multimeters, wire strippers, and Linesman’s pliers.
Explore Related Trades Careers: Construction Electrician, Industrial Electrician, Marine Service Technician
Tools & Materials
Material List
- ~1/2" x 16" x 16" plywood square
- one single gang electrical box (metal) (aka switch box)
- one octagon electrical box (metal) (aka junction box)
- three BX connectors
- ~3' 18/2 thermostat wire (brown jacket, two wires inside)
- one single pole toggle switch (with screws)
- one incandescent holiday light (minimum 3" wires attached)
- eight+ 8x5/8" screws
- one 9V battery
- one 1 1/4" pipe strap
- five+ small wire connector caps (eg. orange Marettes)
- one connector wire with alligator clip ends (or make one with a piece of 18 gauge wire and two alligator clip ends)
- electrical tape
- switch faceplate with screws
Optional:
Tool list
- Linesman's pliers
- wire strippers
- utility knife
- multi screwdriver
- measuring tape
- cordless drill
- driver bits to match all screw heads
- scrap wood to protect work surface
Optional
Procedure
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While you are working, keep your area tidy. Electricians make sure to throw all waste wire bits, including any clippings, into a wire recycling bin. Any loose wire bits can cause short circuits, which allow electricity to flow through an unintended path, which can be a fire hazard.
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Push in the round “KO” or “knockout” circle on the end of the single gang box with your Linesman’s pliers. Wiggle it back and forth or twist until it pops out. -
Remove two KO circles from the octagon junction box as shown. -
Use your wood screws and screwdriver or cordless drill to mount the single gang (switch) box and octagon (junction) box onto the plywood according to the diagram. -
Unthread the ring off the Bx connector and fit the connector into the hole you made in the switch box. Make sure the Bx connector screw is facing up. Thread the ring back on from the inside of the box and twist tightly to secure. -
Measure the distance between your single gang and octagonal box, then add 8”. Cut two pieces of 18/2 brown wire at this length. -
Put the wire on a scrap of wood if you need to protect your work surface. Poke the utility knife into the exterior jacket about 3” up, then pull down to slice the jacket open. Peel it back and trim it short. Repeat at the other end, and for the second piece of wire. -
Use the wire strippers (and the 18-size hole) to strip about 1” of the white and black insulation from the inner wires (8 in total) -
Push the wire ends through the Bx connectors as shown in the plan diagram (one through the octagon box, two through the same BX on the single gang box). Push until about 1” of jacketed wire is in the box, so that when you tighten the connector it is pressing on the jacket and not the internal wires.
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Use a screwdriver to tighten the screws on both BX connectors to hold the wire(s) in place snugly. Pull gently to make sure the wires don’t move. -
Clip your connector wire in half, and strip the last 1” of the insulation from the ends. You will have two matching connector wires: alligator clips on one end, stripped end on the other. -
Push the stripped ends of the connector wires through the bottom BX connector in the octagon box as shown, then tighten the screw to secure the wires. If they are still loose when the screw is tight, loosen it off and add a few small pieces of brown insulation you stripped from the 18/2 to pad the wires. -
Go to your switch box. Use the “loop” hole in your wire strippers to make a hook in the stripped copper ends of both BLACK wires: insert the tip of the wire in the hole and twist the pliers to bend the wire 180 degrees. -
Hook these over the screws on the side of your light switch, then tighten the screws to secure. -
See the Linesman’s Pliers Tool Tutorial for how to splice wire. Line your white wires together so the edge of the insulation lines up. Use your Linesman’s pliers to twist the ends together. Clip the twisted wire so about ½” shows beyond the red insulation. -
Twist on a wire connector cap (Marette). There should be no copper wiring visible (if there is, clip more off the end of the twist). Pull sharply on the wire connector to make sure it’s on snug. -
Tuck all wires and ends into the box, then place the light switch onto the box with the screws facing to the RIGHT (this will ensure that the light is off when the switch is down). Insert the screws to secure the switch to the box. -
Turn your light switch to the OFF position. Add the faceplate if you have one.
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Look to the octagon junction box. Splice the black wire to one of the connector wires (attached to the alligator clip), and the white wires to the other connector wire, as you learned in step 13. Add a wire connector cap to each splice. -
Strip the last 1” of insulation from your light bulb wires, then splice those wires onto the ends of the last piece of 18/2 wire coming from your single gang box. Add wire connector caps. -
Secure your bulb to the plywood by taping down the wires with electrical tape if your wires are long or loose.
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Secure your battery with the pipe strap and two screws, wrapping electrical tape around the battery as necessary to make it snug. -
Clip your alligator clips to the 9V battery terminals, then flick your light switch on. -
Be sure to unclip the alligator clips from the battery whenever your model is not in use, or when you plan to transport it.
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If your light doesn’t come one, try the following:
Check each connection to make sure the wires are twisted tightly and that no copper is showing anywhere in your circuit.
Check the voltage of your 9V with a multimeter, or try a new battery.
Check the light bulb for continuity with the multimeter. If it is an LED and not an incandescent, the 9V may have blown out the bulb.
Prepare the electrical boxes
Mount the boxes
Install the BX connectors
Wire up the boxes
Splicing wires
Test the circuit
Troubleshooting
Extension Challenges
- Make a mini version of this circuit using a smaller type of switch and turn it into a flashlight you can carry. Or, try using a 5mm LED bulb and a 3V battery, and design your own switch.
- Redesign the system so it uses an LED bulb and one or two AA batteries instead (the 9V will likely burn out the LED). If your wires are too thin to use the Marette wire connector caps, simply twist the wires together and cover the bare copper with a piece of electrical tape. Remember: LEDs are directional, so if the bulb doesn’t come on, try wiring it backwards and try again.