I have removed an existing light fitting (broken) - it used terminal blocks to make the connections. I have replaced this with a modern rose. There is a single 3 core cable (twin and earth) from another light fitting/switch (not sure which), 2 way switching. When power is on at the switch the bulb does not light, but there is power registering at the rose and at the lamp holder. Tried different lamp holders and bulbs. This is one of a pair - I have successfully made the change on the first but no luck with the second - any suggestions?