12 volt lights on adjustable stalks over cab seats and rear double bed (1 Viewer)

[Abacist]

Our N & B have 4 of these. The bedroom ones still work but with a bit of persuasion - I imagine the on/off contacts have a bit of corrosion on them. Both lights fitted to the underside of the front bed over the cab seats no longer work.

I would dearly like to take them apart to see if I can fix them but its not obvious how they come apart - can anyone advise please?

Also where might the fuse be for the front ones as that might be the issue?