Interior boot light not working. Bulb OK. No voltage at plug. Where's the switch? Is it the black box behind the bootlid cover? If so how do I get to it? Can it be checked or is it a replacement job? Got all the plastic edge pins out of the'cardboard' cover but the clips on the built-in warning triangle serivetted through the cover. Didn't try to pull too hard in case it broke - and anyway it started raining.