Any number of wires > 2 can be done in a single return journey.

1. Twist pairs of wires together and leave 1 wire (or two for an even number of wires) disconnected.

2. Go to the other end. In the case of an odd number of wires there will be one wire not connected to anything - label it A1. In the case of an even number of wires there are two not connected - label them A1 and A2.

3. Find a pair of wires that 'bell out' and label them B1, B2 (which is B1 and which B2 is arbitary for now). Repeat for C1+C2, D1+D2, etc.

4. Connect A1 to B2, B1 to C2, C1 to D2 and so on. If there are an even number of wires leave the last wire of the last pair, say X1 and A2 unconnected.

5. Back at the original end (room A), untwist the connections, but keep the wires that were paired together.

6. First consider the odd number of wires case. The wire that was not connected to anything is A1, the wire it now bells out to is B2, the wire in the same pair is B1. Now belling from B1 we find C2, and so on till all the wires are labelled.

7. The even number of wires is almost as simple - of the two wires that were left disconnected originally, the one that has no continuity to any other wire is A2, and what remains is the same as the 'odd' case.

The 'one wire' case doesn't need a journey at all.

For the 'two wire' case we only need a single journey and a diode. Or connect a battery between the wires and use a meter at the other end to determine which is + and which is -

Martin Round (nospam@blueyonder.co.uk)