Calling Nosher (Or any other sparky as good as him haha)

[madgaz]

Right, what could be the likely cause of this?
I just can't get my head around it today

Here's the scenario...I have a 2 gang light switch (porch and living room) the porch is one way and the living room is 2 way.
In the back of the switch there 'seems' to be a seperate feed to each switch as opposed to the usual bridging.
Then a switched live to the porch and the 2 way cables for the living room.
If I switch any 1 by its self they seem to work fine however...
...if I switch the living room light on when the porch light is switched on it goes very very dim (almost not on)
Does what I am saying make sense to you?
What could be the most likely cause?

Please please please help...it's driving me nuts.

[Chris_de_Bear]

...if I switch the living room light on when the porch light is switched on it goes very very dim (almost not on)

Do both go very dim, or just 1 ?

Sounds like volt drop under the extra load of driving both sets of lights. Since lights are normally very low power, You'd either need the wire to be EXTREMELY thin or long, or a bad connection somewhere. Could be in the live feed or the neutral (assuming they're common to both sets).

Tell tale sign of a bad connection is overheating at that joint - darkened wire, dull oxidised copper etc.

[madgaz]

Oops...it is only the living room light that dims.

[Nosher]

Sounds deffo like a poor connection bud.
When you have a poor connection it causes allsorts of wierd senarios.
Cant be more specific without being there mate, sorry and all that.

BTW, car electrics are even worse to locate faults

[madgaz]

car electrics are even worse to locate faults

Don't I know it : Owned enough French cars in my time

I've checked all connections available and not managed to rectify the fault that is why I turned to you lot for help
Do you reccon it could be a faulty switch?
Gonna borrow a spare off the father-in-law tomoorow to check.
Con unit is fine, light fittings are fine and switch is fine. All wires buzz out OK but that doesn't mean to say they are 100% does it?

Been about 5 years since I touched anything like this and the amount of beer I have drunk and/or lack of sleep I have had in 5 years seems to have fried my brain :'(

[bazza2541]

Put your multimeter, (set to ac volts) across the live and neutral terminals of the dim light. Tell me what the voltage drops to when you switch both lights on.
Sounds like you have a drain, maybe live and neutral are shorted out somewhere.