I had an issue with a brand new Z21 Black! Very unusual I was told but a new one was eventually sent by Rails of Sheffield. I phoned Gaugemaster and they were really helpful. They have a much clearer guide to the Z21 than the instructions you get in the box.
I had help from a friend, via Whatsapp, on connecting it up.
Here is the link:-
http://www.z21.co.uk/articles/z21-getting-started.html