Turn on old lover with call (6)
I believe the answer is:
excite
'turn on' is the definition.
(I know that turn on can be written as excite)
'old lover with call' is the wordplay.
'old lover' becomes 'ex' (an ex-lover).
'with' is a charade indicator (letters next to each other).
'call' becomes 'cite' (citing is a kind of calling).
'ex'+'cite'='EXCITE'
(Other definitions for excite that I've seen before include "Thrill" , "Send" , "cause a stir" , "Stimulate - arouse" , "Stir up, stimulate" .)