Adding light to existing switch

[Shlomi]

Hi I know I'll be scolded for experimenting without proper knowledge and will be probably be told to call an electrician but I just have to get some insight. Been doing this sort of stuff by myself for a very long time and yet I find myself baffled by this simple electric scenario. I've got an existing switch which controls the bathroom light. We recently had an old water tank removed from the batjeroom so I'm making a storage cupboard for my missus and thought I'd surprise her with a light inside the cupboard controlled by the bathroom light switch so they both come on simulatsnosuly. Managed to get a twin 2.5mm wire from the switch into the cupboard and connected to a new pendant light inside the cupboard. Very pleased. The existing switch has one cable with red and black wires connected to a 2 way switch with the black being the live wire shown by my electricity detector and the red probably the neutral. I've connected my new wire as follows: blue to existing red (neutral) and brown to black (live). The result is most baffling. When I switch the light on the bathroom lights come uon but not the cupboard. When I switch the lights off the cupboard comes on but not bathroom. I've swapped the wires around but no luck, same result. I assumed that switching on will send current to both lamps but clearly that's not the case. What is happening? I should add there's another switch a meter away to control the adjacent bedroom light if that helps to assess.

I'd appreciate any solution to achieve the desirable outcome.

Thanks! Shlomi

[Someone-Else]

I for one would like to see you post the results of your hard safe work, would you expect a chef to use a carrot to find out how hot something is? of course not, he would use the right tool for the right job, so why are you using "an electricity detector" why are you using 2.5 mm cable for a lighting circuit, why are you using a 2 way switch ?

I admire your efforts, but you should bear in mind that "Electricity has no prejudices, it will kill anyone" you really do need to do some more research into what you are doing and get a decent 2 probe testing device.

As you yourself said

I know I'll be scolded for experimenting without proper knowledge

[yartin]

I am not an expert, but 2.5mm cable is a bit too much for a lighting circuit, 1.5mm or even 1.0mm should do.

I would connect the cable to the existing light in the bathroom and not to the switch, ie: have 2 lights in parallel.

Disconnect the cable from the switch and wait to what forum experts say.

Whatever you do make sure the rcd or the fuse/mcb of the lighting circuit is off at the consumer unit / fuse box.

[Shlomi]

Apology for my ignorance but I lack the terminology. But I can assure you that I'm being safe. I always switch the relevant circuit off while working on the switch. My 'electricity detector' is a voltage tester like this [https://amzn.eu/d/a0ANaLb]. It beeps very fast when I touch the hot wire. I hope it's more reliable than a carrot..

In any case I understand that connecting to bathroom lights directly will make more sense. But what could explain that connecting to the switch makes the on-off switch the lights in alternating fashion? Is it the 2.5mm cable? Is it the two way socket?

With regards to the 2 way, it was there already so I just added another wire. I undedatnad the 2.5mm is an overkill but can it cause an issue?

Thanks

[Shlomi]

Quick update problem solved. Left the switch well alone, went for the lights extended 1.5mm wire thru the ceiling to the desired fixture point, connected with wagos in a wago box above the first light ceiling. Very happy and alive

[yartin]

Apology for my ignorance but I lack the terminology. But I can assure you that I'm being safe. I always switch the relevant circuit off while working on the switch. My 'electricity detector' is a voltage tester like this [<span class="skimlinks-unlinked">https://amzn.eu/d/a0ANaLb</span>]. It beeps very fast when I touch the hot wire. I hope it's more reliable than a carrot..

In any case I understand that connecting to bathroom lights directly will make more sense. But what could explain that connecting to the switch makes the on-off switch the lights in alternating fashion? Is it the 2.5mm cable? Is it the two way socket?

With regards to the 2 way, it was there already so I just added another wire. I undedatnad the 2.5mm is an overkill but can it cause an issue?

Thanks

Correct if am wrong but from what I understood see drawing below, the black diagram is what you have "almost", the red is your addition, where is the sense in that?

Untitled.png (25.37 KiB) Viewed 332 times

[yartin]

Quick update problem solved. Left the switch well alone, went for the lights extended 1.5mm wire thru the ceiling to the desired fixture point, connected with wagos in a wago box above the first light ceiling. Very happy and alive

Photos?