They consisted of four carriages - a second class driving trailer , a second class trailer , a second class motor car ( with guard 's \/ luggage compartment above which the pantograph was mounted ) and a composite ( 1st and 2nd class ) driving trailer . They consisted of four carriages - a second class driving trailer , a second class trailer , a second class motor car ( with guard 's \/ luggage compartment above which the Stone Faiveley AMBR pantograph was mounted ) and a composite ( 1st and 2nd class ) driving trailer .