Right in the old harness (4)
I believe the answer is:
yoke
'harness' is the definition.
(I've seen this before)
'right in the old' is the wordplay.
'right' becomes 'ok' (both are affirmative answers).
'in' is an insertion indicator.
'the old' becomes 'ye' (resembles a historical spelling of 'the').
'ok' placed inside 'ye' is 'YOKE'.
(Other definitions for yoke that I've seen before include "Oppressive power" , "Burdensome restraint or oppression" , "Oxen harness" , "Enslave" , "Span (oxen)" .)