Switch on back of appliance is green, possibly (8)
I believe the answer is:
energise
'switch on' is the definition.
('switch on'->'energize' is in my internal thesaurus and 'ize'->'ise')
'back of appliance is green possibly' is the wordplay.
'back of' suggests the final letters.
'possibly' indicates an anagram.
The last letter of 'appliance' is 'e'.
'is'+'green'='isgreen'
'isgreen' with letters rearranged gives 'nergise'.
'e'+'nergise'='ENERGISE'
(Other definitions for energise that I've seen before include "Activate" , "Motivate" , "Stimulate activity" , "Give active force" , "give vigour" .)