Box puts weight under vehicle (6)
I believe the answer is:
carton
'box' is the definition.
(I know that carton is a type of box)
'weight under vehicle' is the wordplay.
'weight' becomes 'ton' (unit of weight).
'under' says to put letters next to each other.
'vehicle' becomes 'car' (car is a kind of vehicle).
'ton' after 'car' is 'CARTON'.
'puts' is the link.
(Other definitions for carton that I've seen before include "He did a far, far better thing" , "Box made of cardboard" , "Box without great strength" , "Sydney -, Tale of Two Cities hero" , "A cardboard container as for milk" .)