Lights finally low, central heating on, kiss and cuddle (6)
I believe the answer is:
smooch
'kiss and cuddle' is the definition.
(I've seen this before)
'lights finally low central heating' is the wordplay.
'finally' suggests the final letters.
'low' becomes 'moo' ('moo' can be a synonym of 'low').
'central heating' becomes 'ch'.
The last letter of 'lights' is 's'.
's'+'moo'+'ch'='SMOOCH'
'on' is the link.
(Other definitions for smooch that I've seen before include "Snuggle" , "Kiss and caress slangily" , "neck" , "Canoodle" , "Dance slowly while in an embrace - kiss - pet" .)