I have 3, 2 way switched lights in my garage and want to add another light but to be 1 way switched. I have run a 2 core and earth cable from the new light into one of the switch boxes and have changed the single switch for a double 2 way switch and re-connected the main lights back as they were in the original single switch. My question is how do I wire in the 2 core and earth from my added light into the other one of the switches or do I need to run in 3 core and earth instead?