The diagram shows the common method of wiring an intermediate switch into a two way light switch circuit. This page shows it wired in the old cable colours if your house has the new colours you want to go here.

Intermediate Switch 4 Way Switch Construction Working
Intermediate switch wiring diagram uk. Simply connect all the wires according to the wiring diagram. This is because there is no dedicated connection for this on the intermediate switch. This allows a single light to be turned on or off from any of the switches. This video also shows how an intermediate switch works. If replacing an existing switch note the location of the terminals and the colour and position of cable connections. To wire a three way lighting circuit you will need 2 two way switches and an intermediate switch.
Here we have a 3 way switching lighting circuit sometimes called two way switching with intermediate. Note that you will have to use a push in connector or any other regular connector to connect the brown wires together. Now it is time for the intermediate switch to be wired up. Intermediate switches can be used for 1 and 2 way switching. Do not forget to connect the earth conductors to the earth terminal provided. In a previous video i showed how a two way.
Finally connect the third switch which is a two way switch to the second length of the 3 coreearth cable. The intermediate switch wiring should look like this. Connect the black wire to the l1 terminal the grey wire to the l2 terminal and the brown wire.