How many driving aids there are on the wagon (8)
I believe the answer is:
teetotal
'on the wagon' is the definition.
(on the wagon can mean abstaining from alcohol)
I don't understand the remainder of the clue.
(Other definitions for teetotal that I've seen before include "temperate" , "Not touching a drop" , "Abstention from alcoholic drink" , "Eschewing booze" , "Completely abstinent" .)