Box adding weight to vehicle (6)
I believe the answer is:
carton
'box' is the definition.
(I know that carton is a type of box)
'weight to vehicle' is the wordplay.
'weight' becomes 'ton' (unit of weight).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'vehicle' becomes 'car' (car is a kind of vehicle).
'ton' put after 'car' is 'CARTON'.
'adding' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for carton that I've seen before include "Sydney -, Tale of Two Cities hero" , "Box without great strength" , "A cardboard container as for milk" , "Cardboard or plastic container" , "fictional lawyer" .)