I had the same problem on my wife's 03 Micra, no boot light, bulb OK.
Some months prior to this the high level brake lamp broke too. The brake lamp had lost its permanent earth, so I added an earth locally and that sorted it.
Back to the boot light. The +12V was there, but no switched earth. A search on Google said to suspect the loom in tailgate lid at the point it flexes when the boot is open and shut.They were correct, two wires had broken here and two others were about to. Soldering a short bridge to re-joint the wires, with heat shrink sleeving on top, sorted it. All works now.
Good luck.
David H. Jones
February 2009
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