Stop; don't switch on again (5,3)
I believe the answer is:
leave off
'stop don't' is the definition.
'leave off' can be an answer for 'stop' (thesaurus). I am not certain of the 'don't' bit.
'switch on again' is the wordplay.
'switch' becomes 'off' (I've seen this in another clue).
'on' means one lot of letters go next to another.
'again' becomes 'leave' (I can't justify this - if you can you should give a lot more credence to this answer).
'off' after 'leave' is 'LEAVE OFF'.
Can you help me to learn more?
(Other definitions for leave off that I've seen before include "Give over!" , "Cease, or shed garment" , "not eating or drinking" .)