I have a double switch downstairs, a single switch upstairs. In the downstairs, a red wire in each common, joined together, a black in 'one way' on the left switch and the same in the right. Upstairs a red in common, a red in L2 and a yellow in L1. Both lights will come on but will only work with one switch downstairs. When the downstairs switch is turned on, the upstairs switch will turn off and on the upstairs light! Please help, very frustrated.

Are these existing switches that you had a problem with or are you installing switches to new new wiring?

Hi, thank you for your reply. Originally there was a double switch downstairs, a single switch upstairs. After moving in, I replaced the downstairs double with a double dimmer without a problem - never touched the upstairs switch. The double dimmer blew about two weeks ago and so in efforts to repair it, have replaced that with a standard double switch again. The upstairs switch has now also been swapped with a new single since having this problem to make sure everything's 'fresh'. Kind of gave up today. Currently, both lights are on, controlled by one of the downstairs two switches. The landing light can be turned on and off with the switch upstairs but if the switch downstairs is turned off (with both lights being out) then it does nothing. Make sense? :-) Thank you

I am assuming you replaced the upstairs switch and the downstairs switch with 3 way switches. If so,somehow you have crossed the wires connected to the switches. You should have 2 wires called runners going directly from switch to switch. These should go on the non common screws of the 3 way switch, One screw should say common beside it.Power on one switch goes to this screw and the load wire(power going to light when turned on] goes to same screw on the other switch. If you installed single pole switches then you have the wrong switches for you to be able to turn the lights on or off from either location.

Hi Jerro, again thank you for your help! When any replacements have been made, wires have only been reconnected to the same terminals they were taken from. To my knowledge, I don't think any wires have been crossed. Before I posted here, I did suggest to my Mrs that I thought the possibly the switch was wrong... I'm now wondering if it is as you've suggested. On the back of the switch, rather than having two switches with an L1, L2 and a common at OPPOSITE ends, they're both in the same position on both switches. Which makes me think it's wrong. Would you agree? I'll change the switch and see if that works. I'll post back in the next day or two after I've done it and let you know how it went.

Much thanks. All the best,

Michael