How do I replace a light switch?

Short answer

To replace a light switch: shut off the breaker, verify power is off with a non-contact voltage tester, remove the cover plate and switch, photograph and label the wires, transfer each wire to the matching terminal on the new switch (ground to green screw, common/hot to the black screw on 3-way switches, travelers to brass screws), secure the switch, reinstall the plate, restore power, and test.

What you’re doing and why

Most light switches are either single-pole (one switch controls one light) or 3-way (two switches control the same light). Replacing a like-for-like switch is straightforward and usually takes 15–30 minutes. The key is safety and matching each wire to the correct terminal on the new device.

Tools and materials

• Non-contact voltage tester (must-have for safety)
• Screwdrivers: Phillips and flathead
• Wire stripper/cutter (14/12 AWG markings)
• Needle-nose pliers
• Electrical tape and wire labels or masking tape/marker
• Replacement switch (single-pole or 3-way; standard or decorator style)
• New wall plate (optional)
• Pigtail and wirenuts or lever connectors if you need to extend/repair a ground connection

Time: 15–30 minutes
Cost: $2–$5 (basic single-pole), $8–$18 (3-way), $10–$25 (decorator), $15–$50+ (dimmer/smart)

Typical specs (USA)
- Breakers: 15A uses 14 AWG; 20A uses 12 AWG conductors
- Switch rating: 15A, 120/277V (ok on a 20A lighting circuit if controlling ≤15A load)
- Strip length: ~5/8 in (16 mm) unless device shows otherwise
- Ground: green screw; Common (3-way): black screw; Travelers: brass screws

Step-by-step

1. Identify your switch type

   • Single-pole: Two insulated wires plus ground; usually labeled ON/OFF.
   • 3-way: Three insulated wires plus ground; no ON/OFF marking; one black (common) screw and two brass (travelers).

2. Turn off power at the breaker

   • Flip the correct breaker and tape a note on the panel. Don’t trust the switch alone.

3. Verify power is off

   • Remove the wall plate. Use a non-contact voltage tester on the switch screws and all wires in the box. Test your tester on a known live outlet first.

4. Remove the old switch

   • Unscrew the switch and gently pull it forward without stressing wires.
   • Take a photo of the wiring. Label each wire (Line/Hot, Load, Common, Travelers). If you’re unsure which is which on a 3-way, the wire on the black screw is the common.

5. Disconnect wires

   • Loosen terminal screws and remove wires. If wires are push-in (backstabbed), release them via the small slot on the back while pulling gently, or cut and re-strip to fresh copper.

6. Prepare the new switch

   • Use side-screw or clamp-style backwire terminals (preferred) rather than push-in backstabs.
   • Strip to the length indicated on the device (about 5/8"). Form a neat hook for side screws; hook closes clockwise around the screw.

7. Make connections

   • Ground: Bare/green wire to the green screw. If the metal box is grounded, ensure a ground pigtail bonds box and device.
   • Single-pole: One hot feed (Line) on one brass screw, the switched leg (Load to light) on the other brass screw. Either side is fine for single-pole.
   • 3-way: The wire that was on the black screw goes to the new switch’s black (Common) screw. The two remaining traveler wires go to the brass screws (order doesn’t matter). Do not put a traveler on the common.
   • Tighten screws firmly. Many devices list torque (often 12–14 in-lb). Snug, but don’t strip.

8. Reinstall

   • Fold wires back in an accordion pattern to avoid stress. Keep the ground away from live terminals.
   • Align the switch straight; mount screws just snug enough not to bow the plate.
   • Install the wall plate.

9. Restore power and test

   • Turn the breaker on. Test function. For 3-way circuits, test from both switch locations.

Safety and best practices

• Always verify power is off on every conductor in the box. Shared neutrals or multi-wire branch circuits can leave other wires live.
• Replace damaged insulation or nicked copper. If you had to cut wires short, add a pigtail using UL-listed wirenuts or lever connectors.
• Avoid backstab-only connections; they loosen over time. Use screw or clamp-style terminations.
• Keep box fill in mind. Overstuffed boxes can overheat. If it’s very tight, consider a deeper “old work” box upgrade.
• If adding a dimmer or smart switch, confirm LED/fixture compatibility and whether a neutral is required.

Common mistakes

• Not identifying the common on a 3-way and mixing it with a traveler.
• Forgetting the ground connection or leaving it loose.
• Over-tightening device screws so the switch tilts or the plate cracks.
• Reusing oxidized, backstabbed wires without re-stripping to clean copper.
• Installing a dimmer on a circuit with non-dimmable LEDs, causing flicker.

When to call a pro

• Aluminum wiring (look for “AL” on cable or dull gray conductors). You need CO/ALR-rated devices and special practices.
• Old cloth-insulated, brittle, or knob-and-tube wiring.
• Boxes with multiple circuits or handle-tied breakers you don’t fully understand.
• No ground in a metal box, or uncertain bonding/grounding.
• Converting switch types (adding a 3-way where one didn’t exist), relocating boxes, or troubleshooting a dead/shorted circuit.

Quick tip

Label the breaker in the panel while you’re at it. A 50-cent label saves time on your next project.