How to Wire a Light Switch

Knowing how to wire a light switch is important if you’re planning to handle the task on your own. In this guide, we’ll walk you through the process of wiring a basic standard light switch.

How to Wire a Light Switch
How to Wire a Light Switch

For those unfamiliar with the process, wiring a light switch might seem challenging for a do-it-yourselfer. However, it’s a fairly simple task that requires following a few straightforward rules to ensure safety.

In this tutorial, we’ll focus on wiring a one-way switch, which is the most basic type. This involves installing a switch with a single toggle to control the on/off function of one light. If you have a two-way light switch, the process can be more complex and is not covered in this guide.

How to Wire a Light Switch: A step-by-step guide 

Before you begin, gather the necessary tools for the job. You’ll require a specialized electrical insulated screwdriver set, such as the Hilka Electricians Screwdriver Set available on Amazon.

Also, you’ll need:

  • a new light switch.
  • wire strippers.
  • electrical tape.

Ensure you have these tools on hand before starting the task. Also, plan to undertake the work during daylight hours since you’ll be turning off the electricity to your home as part of the process.

1. Turn off the Power:

Before you begin, it’s important to cut off the electricity to ensure you’re not dealing with a live circuit. Locate your fuse box, where you’ll find a large on/off switch. Push it to the “off” position. For added safety, you can also remove the fuse that controls the lighting circuit you’re working on.

Next, confirm that the electricity has indeed been turned off. Test the switch you’re replacing and any other plugged-in electrical items, such as a lamp or TV, to make sure they are not functioning.

2. Remove the old switch:

Use a suitable screwdriver to gently take off the switch plate. Keep the screws in a safe place to avoid losing them. Take note of how the wires are connected and consider taking a photo for reference.

Usually, a one-way switch has two terminals labelled COM (at the top) and L1 (at the bottom). The brown wire (live feed) is inserted into the COM terminal, and the blue wire (switch wire) goes into the L1 terminal.

It’s worth mentioning that the blue wire, despite its colour, is often live and not neutral, as indicated by a brown sleeve or tape.

For older wiring, the red wire (live feed) goes into the top COM terminal, and the black wire (switch wire) goes into the L1 terminal. Once again, the black wire, which may seem neutral due to its colour, might have a red sleeve or tape, indicating that it is also part of the live circuit.

2. Wire up the new switch:

Loosen the screws on the terminals holding the wires in place and gently pull out the wires from the old light switch. Set aside the old switch. Check that the wire ends are neatly twisted together, without any loose strands. Use pliers to tidy them up if necessary.

You might need to strip the wires using wire strippers and trim them with pliers. Leave around 15mm of bare wire and enough length for easy connection to the new switch terminals.

Insert the brown or red wire (live feed) into the COM terminal and tighten it securely. Give it a gentle tug to ensure a tight connection. Repeat the process with the switch’s blue or black wire, placing it into the L1 terminal. If the wires don’t fill the terminals, strip them further back and fold them over for a secure connection.

If you’re installing a light switch with a metal faceplate, like the BG Brushed Steel Light Switch from B&Q, connect the green/yellow earth wire to the faceplate. Once done, tuck the cable into the back box and screw the switch plate back on, making sure it’s secure. Finally, restore power to test the new switch.

What are the ‘New’ Wiring Colours?

The current standard wiring colours, introduced in 2004, are green/yellow, blue, and brown. Since the beginning of 2006, all new wiring installations have had to follow these colours.

However, if your home was built before these regulations took effect, the wiring is likely to be in red, black, and green/yellow (before 1977, the earth wire was just green). The old live red wire was replaced by brown, the old neutral black wire by blue, and the old green earth wire became yellow and green.

It’s crucial to be aware of these colour changes and ensure that you connect to the correct terminal whenever you’re working on any domestic electrical tasks, such as wiring up a light switch or a plug.

The Meaning of L1 and L2 on a Light Switch

A one-way switch usually has a COMMON (COM) terminal at the top and an L1 terminal at the bottom. If it’s a two-way switch, there will be an additional L2 terminal next to the L1 terminal.

Jordan Batchelor from JB Electrical explains the meaning of L1 and L2: “There are two ways to connect a light switch, one way and two way. In a one-way switch installation, you connect the incoming permanent live conductor to the common terminal and the switched live conductor (going to the light fitting) to the L1 terminal.

Two-way switches are used when you have two light switches controlling one light, for example, one switch at both ends of a hallway. In this case, you would use the L2 terminal.”

If you’re changing a light switch, it might be a convenient time to also replace the light fitting since you’ll already have the necessary tools and the power turned off.

Are Switch Markings on a Light Switch all the Same?

No, markings inside switches can vary between manufacturers. Usually, a one-way switch has a COM or COMMON marking next to the top terminal and an L1 marking next to the bottom terminal.

For a two-way switch that can function as a one-way switch, it typically has an extra terminal marked L2 beside L1. However, it’s important to be aware that some manufacturers skip the COM marking and instead label the top terminal as L1 and the bottom terminal as L2 and L3.


How do I know if I can wire a light switch myself?

If you’re comfortable working with electrical components, understand safety precautions, and follow instructions carefully, wiring a light switch can be a manageable DIY task. If unsure, consider consulting a professional electrician.

Can I use any light switch for replacement?

Ensure compatibility by matching the type (one-way, two-way) and features of your existing switch. Pay attention to the manufacturer’s instructions.

Can I replace a one-way switch with a two-way switch?

Yes, but you’ll need additional wiring for a two-way setup. If you’re unsure, consult a professional.



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