Replacing like for like 2 gang 2 way switch , now not workin

[smc999]

I am really lost.
I have replaced all the light switch front plates in my new house( they were brass and the lighting circuit isn't earthed!)and they work fine, except for this one.
Its a 2 way 2 gang switch that is only being used as a 1 way switch. It was wired in the following way.

All wires are red.

Common to common on each switch then one cable to L2 on switch 1 and a piece of cable not attached to anything from L1 to L1.
Now only one of the switches works and the other doesnt. I swapped the L2 on one switch to the other, then that worked and the other didn't?

The other switch that I replaced that was 2 gang and had 4 cables yet this one only has 3 (2 commons and L2)

I'm a complete novice when it comes to electrics and I can't find anything like this using search on these forums. Any help would make the last 3 hours of trying nearly worthwhile.

 

[Lectrician]

You need to be a little more descriptive.

Could you post a pic?

Are there blacks in a terminal block in the back box? (leave them in it).

How many reds to you have from the wall? 3 or 4?

 

[MANDATE]

I would identify the 'live' wire and put this in 'com' on SW1 then a short wire to link 'com' on SW1 to 'com' on SW2.
You should be left with two wires. one to each switch L1 or (L2 if you like)
If you have 4 wires, then there will be 2 which are 'live' and one of these would be used istead of the short link.
If you're a novice, try drawing the terminals and wires to see how the complete circuit is made.

 

[smc999]

Thanks for the quick replies.
There are 3 red wires in total and yes there are black wires in the back of the box that are in a block.
I don't understand why there would be a piece of wire from L1 on one switch to L1 on the other. Is this to complete the circuit? If so it doesn't make the other switch work with or without it.

I will have to work out how to get a picture from my wifes camera onto my pc if the picture would help.

 

[Steve]

Again, find the permenant live wire somehow. This goes to BOTH switches, in the COM terminals - you need a link wire.

Then the 2 other reds are the switched lives to the lights. If there is a link in the L1's, take it out, just use the COM link i explained above, for simplicity's sake.

 

[Lectrician]

Sounds like you have a feed in, and two switched supplies out. The neutrals being blocked in the back of the box.

As stated, the constant live supply needs to connect to BOTH com terminals using a small link of red cable.

The other two reds then go seperately to each of the two L1's

Simple

 

[MANDATE]

smc999. It's quite simple really, you wouldn't run two hose pipes to fill two tanks with water when you can run one hose and then divide it at the tank.
there's no point in running a separate supply of electricity when it's already there at SW1. the link is all you need. If the live went into COM your link would not function until the switch was made. On the other hand you could put the live into L1 and link L1 to L1 and take the two switched lives from COM. It would work ok just that the switch would upside down

 

[smc999]

I take it I need to buy a volt meter or something so I can work out which wire is the constant live one?
Could you tell me what I need to be looking for to find out which one is the live.

Thanks again for all the help.

 

[Lectrician]

smc999. It's quite simple really, you wouldn't run two hose pipes to fill two tanks with water when you can run one hose and then divide it at the tank.
there's no point in running a separate supply of electricity when it's already there at SW1. the link is all you need. If the live went into COM your link would not function until the switch was made. On the other hand you could put the live into L1 and link L1 to L1 and take the two switched lives from COM. It would work ok just that the switch would upside down

It wouldn't operate upside down - it would operate the same..........It would operate upside down if you substituded L1 for L2!

 

[MANDATE]

three wires ones 'live' twos 'dead'. With power off join any two in a terminal block and isolate 3rd wire in another block. put power back on and if no lights work the isolated wire is the live.
If one light works, then one of the two must be 'live'. So identify and swap the isolated wire for one of the two and repeat test,You can then eliminate one of the remaining wires leaving you with the 'live'
You can use either a electricans screwdriver made for the purpose(but don't touch the steel blade)
or a non contact volt stick or a volt meter (but theres has to be a neutral wire present to complete the circuit)

 

[MANDATE]

Your quite right 'Lectrician' my mistake. must be getting confused in my old age.

 

[smc999]

Thanks for that. I'll give it a go tomorrow when its light and I can see what I'm doing and report back.

 

[smc999]

three wires ones 'live' twos 'dead'. With power off join any two in a terminal block and isolate 3rd wire in another block. put power back on and if no lights work the isolated wire is the live.
If one light works, then one of the two must be 'live'. So identify and swap the isolated wire for one of the two and repeat test,You can then eliminate one of the remaining wires leaving you with the 'live'
You can use either a electricans screwdriver made for the purpose(but don't touch the steel blade)
or a non contact volt stick or a volt meter (but theres has to be a neutral wire present to complete the circuit)

Used the terminal block method and I now have 2 perfectly working lights.

Many thanks for all the help, especially MANDATE.