Light Switch Installation Guide

As well as the functional purpose to a light switch, it also has an aesthetic role in setting the mood of a room. You might want to upgrade to a vintage brass switch or a modern brushed chrome one, for example. Alternatively, you might just want to replace a broken switch in a garage or utility room with something cheap and cheerful, like a basic white plastic light switch. This article will tell you how to do it.

Two-way and one-way switches

This guide is about replacing a basic one-way switch, which is a normal switch that just operates a single light, or more than one light simultaneously (e.g. two wall lights). Its “on” and “off” positions never change. A two-way switch is one that controls a light (often a landing light) but where there are two switches on the same circuit. That means you can turn the landing light on and off both from the hall and from the landing. The position of the switch will not indicate whether a light is on or off, as it depends on the position of the other switch. We deal with two-way switches in another article which you can read here. 

Dimmer switches

If you have dimmer switches that have been in place for several years, they might well be the old type for incandescent (tungsten or halogen) bulbs. LED dimmer switches operate differently, so you must make sure that you use a switch designed for dimmable LED bulbs. Since the sale of halogen lights was banned in the UK in September 2021, you might find it hard to find a traditional dimmer switch. We’d always recommend going to LED anyway as they are much more efficient. Normal (non-dimmable) switches are not affected.

How to install a light switch: our step-by-step guide

1. Make it safe

Electricity is dangerous. If you’re in any way not confident about getting behind the switch, please get in touch with someone who is – preferably a qualified electrician. However, if you’re comfortable with basic electrics, replacing a switch is one of the “like for like” tasks you can do as a homeowner under Electrical safety: Approved Document P of the Building Regulations.

If the switch and light are working, switch it on, then go to the consumer unit (often known as a fuse box).

Your consumer unit will have different circuits indicated, for example “upstairs lights” and “downstairs sockets”. You can just isolate the particular switch you’re working on, but light switches can be a little different, and a switch might be connected to two different circuits. For that reason, we’d recommend turning the mains off altogether. You might have to reset a few clocks and timers, but it’s better than taking a risk with 230 volts.

Return to the switch, and if the light is now off, you can be 99% sure you’re safe.

2. Remove the faceplate

Using a screwdriver, undo the faceplate, which is usually attached with two screws. Pull it clear firmly, but don’t tug too hard as you don’t want to damage the wires. If you have a voltage detector, check there’s no current following the manufacturer’s instructions.

3. Take a note of the wiring and the back box or pattress

Have a good look at the way the wiring is connected to the face plate. You might need to use a torch. Write down which terminal each wire connects to, which should be:

  • Brown or Red → Common terminal
  • Blue or Black → L1 terminal
  • Green and yellow→ Earth terminal (⏚)
  • If there’s a metal mounting box in the wall, there should also be a sheathed earth wire running from the earth terminal on the switch to the earth connector earth on the mounting box.

It’s a good idea to take photos, just to be double sure.

Note: if there is no Earth cable, it’s probably an old switch, or hasn’t been placed by a qualified electrician. We’d recommend you stop right now and seek professional help.

4. Remove the wires

Using a VDE screwdriver (a special screwdriver designed to be electrically safe), undo the terminal screws on the back of the faceplate. If there’s an Earth cable running to the electric socket box, you only need to disconnect it from the faceplate, not the box.

5. Connect the wires to the new switch

Note where the terminals on the new switch are, as it’s possible they are in a different place. Use the letters and symbols, not the position. If your switch has a top and a bottom, make sure it’s the right way up. Now reconnect:

  • Brown or Red → Common terminal
  • Blue or Black → L1 terminal
  • Green and yellow→ Earth terminal (⏚), but don’t tighten the screw
  • Push the extra Earth cable coming from the back box to the Earth terminal and tighten it.

Give each wire a firm but measured tug to make sure it doesn’t come out.

6. Replace the faceplate

Now, replace the faceplate by putting it back in place and tightening the screws.

7. Turn on the power

Go back to the consumer unit and turn on the main power and the circuit switch, if you turned that off too. When you return to the room you’ve been working in, the light may be on or off (as the switch might be in the “on” or “off” position). Flick the switch to check it has been connected correctly. 

If you’re sure you did everything right, and the light does not work, either you have got a faulty switch, have bought the wrong type of switch, or have damaged the cabling. It’s best to get in touch with a qualified electrician, who will probably be able to sort it out in no time.