Lights, say, not working? Almost completely (5)
I believe the answer is:
offal
'lights' is the definition.
(I've seen this before)
'not working? almost completely' is the wordplay.
'not working?' becomes 'off' (I've seen this in other clues).
'almost' means to remove the last letter (most of the word but not all of it).
'completely' becomes 'all' ('all' can be a synonym of 'completely').
'all' with its last letter taken off is 'al'.
'off'+'al'='OFFAL'
'say' acts as a link.
(Other definitions for offal that I've seen before include "Bits of waste meat" , "Rubbishy bits of animal flesh" , "Butcher's leftovers" , "Waste parts of a carcass" , "Less valuable edible parts of animal" .)