Trader so drunk in motor vehicle (8)
I believe the answer is:
roadster
'motor vehicle' is the definition.
(I know that roadster is a type of motor vehicle)
'trader so drunk' is the wordplay.
'drunk' indicates anagramming the letters.
'trader'+'so'='traderso'
'traderso' is an anagram of 'ROADSTER'.
'in' is the link.
(Other definitions for roadster that I've seen before include "Small open-top car" , "Open two-seater car" , "An open car without rear seats" , "sporty vehicle" , "Open-topped car" .)