Some of the un-switched lampholders need to have the 3 parts lined up or the lamp will not work when connected. This is an issue with the series of 1000 lampholders due to their design. Please make sure these parts are aligned.
There are indents on the side of the 3 parts and these must all line up together.
When fitted you can check like this. The 2 slots of the lampholder will be 180 deg. from the 2 pins. This is what you need to ensure the contact of the lamp makes contact to the lampholder.