Andy Wade wrote:

On 24/03/2011 23:22, Ronald Raygun wrote:
However, there is a solution involving two double pole changeover
switches.

Surely you can do it with two single-pole changeover (SPDT) switches.
Using your terminal naming, so SW1 has 'fixed' contacts A1 & A2 and
common or moving contact A (and SW2 similarly has B1, B2 and B). Now
connect

- A1 and B1 to -ve supply
- A2 and B2 to +ve supply
- A and B to the outgoing wires X and Y.

If both switches are 'up' or 'down' X & Y are connected to the same
supply pole, so both lights are off. If one is up and the other down
there will be an output to X & Y, with the polarity dependent on which
switch is up.

QEF

Ah yes, well done. Why didn't I think of that?

What I had was two DPDT switches. Using the same notation, one switch
has moving contacts A and B which it switches either to A1 and B1 or to
A2 and B2, with the other switch using the letters C and D correspondingly.

I connect A1 and C1 to +, and B1 and D1 to -.
I connect A to C, and B to D.
I connect X to A2 and D2, and Y to B2 and C2.

Call each switch "off" when it is in the "1" position, i.e. A=A1, etc,
and "on" when in the "2" position, i.e. A=A2, etc.

When both switches are "off", X and Y are not connected to anything.
When both switches are "on", + and - are not connected to anything,
but X and Y are conncted harmlessly to each other.
When at least one switch is "off", A and C are connected to +, and
B and D are connected to -.
When at least one switch is "on", X is connected either to A and hence +
or else to D and hence -, depending on whether switch AB or CD is on.
Correspondingly Y would be connected to B and hence - or to C and hence +.

QEF, eh? I like it.