Old vehicle Ian exchanged for an instrument (7)
I believe the answer is:
ocarina
'for an instrument' is the definition.
(ocarina is a kind of instrument)
'old vehicle ian exchanged' is the wordplay.
'old' becomes 'o' (abbreviation).
'vehicle' becomes 'car' (car is a kind of vehicle).
'exchanged' indicates anagramming the letters.
'ian' with letters rearranged gives 'ina'.
'o'+'car'+'ina'='OCARINA'
(Other definitions for ocarina that I've seen before include "Toy flute" , "Small egg-shaped wind instrument with holes for the fingers" , "Bird-shaped flute" , "Wind instrument with a mouthpiece and finger holes" , "Simple wind instrument" .)