Sign of nerves following car smash in the North (6)
I believe the answer is:
arctic
'north' is the definition.
(thesaurus)
'sign of nerves following car smash' is the wordplay.
'sign of nerves' becomes 'tic'.
'following' is a charade indicator (letters next to each other).
'smash' is an anagram indicator.
'car' is an anagram of 'arc'.
'tic' put after 'arc' is 'ARCTIC'.
'in the' is the link.
(Other definitions for arctic that I've seen before include "The frozen north" , "Of area round N. Pole" , "It's cold at the top" , "Very cold as in the far north" , "Extremely cold" .)