... till sightseer crashed into vehicle (4,8)
I believe the answer is:
cash register
'till' is the definition.
(cash register is a kind of till)
'sightseer crashed into vehicle' is the wordplay.
'crashed' is an anagram indicator.
'into' indicates putting letters inside.
'vehicle' becomes 'car' (car is a kind of vehicle).
'sightseer' anagrammed gives 'shregiste'.
'shregiste' put inside 'car' is 'CASH-REGISTER'.
(Other definitions for cash register that I've seen before include "Machine used in shops" , "Shop till" , "money machine" , "one may advise change" .)