draw what you (think you) did. There are many ways this could be weird. Many^2 if there are more switches than lights.

>>2549

>>2548
>When light B is turned on light A goes off.
Does the reverse also happen?

>>2551

Nope. B works whether A is on or off.

>>2552

Have you accidentally used a double throw light switch at B?

The only thing I can think of is maybe light A has a higher resistance than B. I could try swapping the bulbs. I need to take up the floorboards and reconnect light A though because I got worried and disconnected it.

>>2553

Not sure. But how would that cause a problem?

>>2554

I think you've just wired up the wrong terminals on a two-way switch. Do you own a multimeter?

http://wiki.diyfaq.org.uk/index.php/2_Way_Switching

>>2556

I'll check it. Does the live "input" cable go in the L or C terminal?

>>2557

C is your live/input voltage - I bet that's what you've done, put in in an L. This would mean that switch A is only receiving live (common) power when B is switched on.

>>2559

lies

>>2560

Sorry.

Solved it now, I wired it into the to mains instead

It's a light in a little bike-shed in our porch where we have a motion sensitive light plugged into the mains. I used a junction box to wire both lights into the same plug.

The plug is fitted with a 3 amp fuse. Is that too much? Should I use a 1 amp?

>>2572

A 100w bulb only draws about 400mA, so a 1A fuse is probably the best option.

1A fuses are hold to get hold of in the size that will fit in a plug. Most of the 1A fuses you'll find for sale will be a smaller fitting that's usually used for shaver sockets.

3A is fine. It's there to protect the wiring not the bulb itself, and you almost certainly don't have 1A wires unless you've bought some dodgy lights off a chinese ebay seller.