Help Tracing a wire

I have just moved into a house and I have found near the back door that there are 3 mains cables sticking out of a wall where a switch unit clearly once was. The wires are labled up as being for outside lights. I would like to put external lights on the property just the other side of the wall from these wires. I have tested them and none of them appear to be live. My question is, what is the easiest way to trace where these wires goes so I can see about the possibility of making these wires live again. I will be using a qualified electrician to conduct any work however if I can trace these wires prior to calling them out it will help keep costs down. Please note I have no electrical qualifications so please keep answers as simple as possible. Thank you in advance for any advice you can offer.