Turn on debtor that's ready for it after bit of petting (5,2)

'ready for it after bit of petting' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'turn on debtor' is the wordplay.
'turn' becomes 'pup' (I can't explain this - if you can you should believe this answer much more).
'on' means one lot of letters goes inside another (as in clothing \'on\' a person).
'debtor' becomes 'ower'.
'pup' going around 'ower' is 'POWER UP'.

'that's' is the link.

Can you help me to learn more?