Vehicle with nothing working? That's a joke (7)
I believe the answer is:
cartoon
'that's a joke' is the definition.
(a cartoon is a humorous comic strip)
'vehicle with nothing working?' is the wordplay.
'vehicle' becomes 'cart' (cart is a kind of vehicle).
'with' says to put letters next to each other.
'nothing' becomes 'O' (O resembles 0).
'working?' becomes 'on' (on can mean working or activated).
'cart'+'o'+'on'='CARTOON'
(Other definitions for cartoon that I've seen before include "could make one laugh" , "Humorous drawing or film of a succession of them" , "Amusing or satirical drawing" , "Humorous or satirical drawing" , "Comic strip" .)