Red vehicle left in position (7)
I believe the answer is:
scarlet
'red' is the definition.
(synonyms)
'vehicle left in position' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'position' becomes 'set' (set is a kind of position).
'car'+'l'='carl'
'carl' going within 'set' is 'SCARLET'.
(Other definitions for scarlet that I've seen before include "immoral" , "Shade of red" , "Let cars be this colour" , "Fallen" , "Clarets (anag.)" .)