An Indian instrument is wrong for Jack (5)
I believe the answer is:
sitar
'an indian instrument' is the definition.
(I've seen this before)
'is wrong for jack' is the wordplay.
'wrong' indicates anagramming the letters.
'for' means one lot of letters go next to another.
'jack' becomes 'tar' (I've seen this before).
'is' anagrammed gives 'si'.
'si'+'tar'='SITAR'
(Other definitions for sitar that I've seen before include "Lasting from morning to night" , "Long-necked musical instrument of India" , "music-maker" , "instrument out east" , "Guitar-like instrument" .)