Pool lights with just two 12v wires in the switch

[santycg]

Hello everyone. Let's see if someone can give me a hand with this.

The lights in my pool don’t have an independent electrical panel. They turn on and off with a switch located inside the house.
There is a safety transformer that converts to 12V, and the cables coming out of the transformer (12V) pass through the wall switch to turn the lights on and off. Then (I imagine) they go directly to the lights.

I’ve managed to install Shelly relays for the ceiling lights “without issue” (I put that in quotes because the tangle of wires is tricky to figure out at first), but in this case, with 12V and without a neutral wire going directly to the lights, it’s even harder for me to understand.

Here’s how the circuit is currently set up—or at least what I can see by opening the switch, the junction box, and the area where the transformer is located:

The wall switch has a neutral wire and a brown wire connected to it. Both, I assume, come from the transformer because they already carry 12V, not 230V.

What I want is to automate the pool light using a Shelly (Plus 1, or any other suitable one). But I don’t know how to do it with only these two 12V wires.

I don’t mind if the wall switch becomes unusable and I can only control it via the Shelly. Ideally, though, I’d like both to work (so I can turn it on with the Shelly and off with the switch, or vice versa), but I’m not sure if that’s possible in this case.

I understand that the Shelly needs to be "powered" first, using neutral and live wires from somewhere, to function. But then I don’t know what to do to make those 12V cables pass through the Shelly.

With ceiling lights, there are hundreds of diagrams online, and it’s more “straightforward,” but this specific case is beyond me.
If you need a diagram of the current circuit, I can try to draw one.

I’m trying to set up a circuit to test it, to see if I can figure it out step by step, but since it’s 12V, it’s more complicated for me. I’d need to buy a 12V transformer, etc.

Thanks!

[thgoebel]

Sometimes we have to handle with black boxes. Like in this scenario. But it is possible:

If I understand you correctly, you‘ve two wires and a switch. The latter is used to switch pool lights on and off. Lights are supplied with somewhat like small voltage…

As shown above, we use a Shelly plus 1 (or the brand new Shelly 1 Gen3). Both devices have dry contacts which are SELV proof. But for double safety, we supply the Shelly with an extra SELV proof DC power supply, which delivers the 12V DC (stabilized!) for the Shelly. Optionally, you may use the existing switch, properly wired, to switch the SW input of the Shelly.