First let me say that although I an electrical and computer engineering student (NTUA, Greece), I have been so focused in the "computer" part I have very little knowledge of electrology and even that is mostly theoretical. I do know how to use some very basic tools (multimeter, which I currently don't have, and, ahem, screwdriver) and once I put together a filter circuit that almost worked, but beyond that it wouldn't be exaggerating to say my only practical experience in such matters has been changing light bulbs.
Now, my problem is this:
I am currently staying in Chisinau, Moldova, which is a former Soviet Union country. In our kitchen there is a light as well as a ventilator. They are both controlled by what I believe was meant to be a common DPST switch.
When I arrived there was only a hole in the wall with three identical (well, one is a bit longer but I doubt that's significant) white cables in it. The light was turned on by sticking your hand in and connecting two of these cables (the short ones, actually). If you wanted the ventilator to function you connected the third (long) cable as well.
Not very safe, I thought, so with my limited knowledge I successfully (!) installed a two-button switch to control the light. I left out the third (long) cable, so the second button does nothing and there is now no way to turn on the ventilator.
I now want to connect the third cable too and make the switch fully functional.
This is my guess at what's going on inside the walls (maybe "neutral" and "hot" should be inversed):
Connections AC and ABC have been tested and BC is also presumed to be safe.
What I am concerned about and the reason why I am hesitating is this:
I have no way of telling which cable is C (it is logical it should be the middle one, but is that a rule?) and which is A, so it is possible A and B could be accidentally connected.
My question (finally!) is this:
Is it safe to connect AB (or BC, remember I can't tell) and see what happens?
If I understand correctly C is "hot" while A and B are "neutral" and you need two "hot" cables to get something wrong. In any case it seems to me there is no way to get a "wrongly" closed circuit. At worst I'll end up with an open circuit.
Is this correct? Should I proceed through trial and error or should I get a multimeter and/or call a professional?
Many thanks in advance and sorry for the long post!
Your help is greatly appreciated!