Thanks for your reply. I'm looking at the diagram and what I've done and can't quite figure out what I need to change.
From what you have said, it sounds like I need to retain the original connection from the DC plug to the light, but then I don't know how the switches are incorporated.
At the moment, red wire goes from power to com switch 1, from com switch 1 to com switch 2 and then light. Black goes to nc switch 1, from nc switch 1 to nc switch 2 and then light.
One cable from power to switch 1, two cables from switch 1 to switch 2 and one cable from switch 2 to light.
Have I unnecessarily added two rather than one cable from switch to switch? Should I have two cables from power, with one black and red going straight to light and the other going to switch one then switch two? What then?