Radar not working to pin down one Aussie convoy (4,5)
I believe the answer is:
road train
'aussie convoy' is the definition.
'radar not working to pin down one' is the wordplay.
'working' is an anagram indicator.
'to pin down' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'radar'+'not'='radarnot'
'radarnot' is an anagram of 'roadtran'.
'roadtran' enclosing 'i' is 'ROAD TRAIN'.
(Other definitions for road train that I've seen before include "truck with trailers" , "means of moving freight" , "See Aussie truck" , "Antipodean lorry with trailers" .)