I sincerely lean more about what Daniel says. I had a Peugeot 406 and the same thing happened to you. It was the cable under the seat, there were times when the seat moved or if it was touched by what was turned on the happy light, in the workshop to which we carried it they turned off the light with the machine. What is important is that when it comes to passing the ITV, at least in Spain, you turn it off since otherwise it would not happen.
Obviously I am not saying that what WTO Electro says is not true, but I talk about my experience and since we put ourselves we are going to discard the easiest. Greetings